返答ありがとうございます！とりあえず結果はこのようになりました。
他の質問を見たときこのような文があったと思うのですが、実際どのように見たらいいのか
さっぱりなもので・・・

00:00.0 Host bridge: Advanced Micro Devices [AMD] RS780 Host Bridge
    Subsystem: Hewlett-Packard Company Device 30e4
    Flags: bus master, 66MHz, medium devsel, latency 0
    Capabilities: [c4] HyperTransport: Slave or Primary Interface
    Capabilities: [54] HyperTransport: UnitID Clumping
    Capabilities: [40] HyperTransport: Retry Mode
    Capabilities: [9c] HyperTransport: #1a
    Capabilities: [f8] HyperTransport: #1c

00:01.0 PCI bridge: Advanced Micro Devices [AMD] RS780 PCI to PCI bridge (int gfx)
    Flags: bus master, 66MHz, medium devsel, latency 64
    Bus: primary=00, secondary=01, subordinate=01, sec-latency=0
    I/O behind bridge: 00005000-00005fff
    Memory behind bridge: 54100000-542fffff
    Prefetchable memory behind bridge: 0000000040000000-000000004fffffff
    Capabilities: [44] HyperTransport: MSI Mapping Enable+ Fixed+
    Capabilities: [b0] Subsystem: Advanced Micro Devices [AMD] RS780 PCI to PCI bridge (int gfx)
    Kernel modules: shpchp

00:04.0 PCI bridge: Advanced Micro Devices [AMD] RS780 PCI to PCI bridge (PCIE port 0)
    Flags: bus master, fast devsel, latency 0
    Bus: primary=00, secondary=02, subordinate=02, sec-latency=0
    I/O behind bridge: 00003000-00004fff
    Memory behind bridge: 53000000-540fffff
    Prefetchable memory behind bridge: 0000000050000000-0000000050ffffff
    Capabilities: [50] Power Management version 3
    Capabilities: [58] Express Root Port (Slot+), MSI 00
    Capabilities: [a0] Message Signalled Interrupts: Mask- 64bit- Queue=0/0 Enable+
    Capabilities: [b0] Subsystem: Hewlett-Packard Company Device 30e4
    Capabilities: [b8] HyperTransport: MSI Mapping Enable+ Fixed+
    Capabilities: [100] Vendor Specific Information <?>
    Capabilities: [110] Virtual Channel <?>
    Kernel driver in use: pcieport-driver
    Kernel modules: shpchp

00:07.0 PCI bridge: Advanced Micro Devices [AMD] RS780 PCI to PCI bridge (PCIE port 3)
    Flags: bus master, fast devsel, latency 0
    Bus: primary=00, secondary=03, subordinate=05, sec-latency=0
    I/O behind bridge: 00002000-00002fff
    Memory behind bridge: 52000000-52ffffff
    Prefetchable memory behind bridge: 0000000051000000-0000000051ffffff
    Capabilities: [50] Power Management version 3
    Capabilities: [58] Express Root Port (Slot+), MSI 00
    Capabilities: [a0] Message Signalled Interrupts: Mask- 64bit- Queue=0/0 Enable+
    Capabilities: [b0] Subsystem: Hewlett-Packard Company Device 30e4
    Capabilities: [b8] HyperTransport: MSI Mapping Enable+ Fixed+
    Capabilities: [100] Vendor Specific Information <?>
    Capabilities: [110] Virtual Channel <?>
    Kernel driver in use: pcieport-driver
    Kernel modules: shpchp

00:11.0 SATA controller: ATI Technologies Inc SB700/SB800 SATA Controller [AHCI mode] (prog-if 01)
    Subsystem: Hewlett-Packard Company Device 30e4
    Flags: bus master, 66MHz, medium devsel, latency 64, IRQ 5
    I/O ports at 6018 [size=8]
    I/O ports at 6024 [size=4]
    I/O ports at 6010 [size=8]
    I/O ports at 6020 [size=4]
    I/O ports at 6000 [size=16]
    Memory at 54309000 (32-bit, non-prefetchable) [size=1K]
    Capabilities: [60] Power Management version 2
    Capabilities: [70] SATA HBA <?>
    Kernel driver in use: ahci

00:12.0 USB Controller: ATI Technologies Inc SB700/SB800 USB OHCI0 Controller (prog-if 10)
    Subsystem: Hewlett-Packard Company Device 30e4
    Flags: bus master, 66MHz, medium devsel, latency 64, IRQ 10
    Memory at 54308000 (32-bit, non-prefetchable) [size=4K]
    Kernel driver in use: ohci_hcd

00:12.1 USB Controller: ATI Technologies Inc SB700 USB OHCI1 Controller (prog-if 10)
    Subsystem: Hewlett-Packard Company Device 30e4
    Flags: bus master, 66MHz, medium devsel, latency 64, IRQ 10
    Memory at 54307000 (32-bit, non-prefetchable) [size=4K]
    Kernel driver in use: ohci_hcd

00:12.2 USB Controller: ATI Technologies Inc SB700/SB800 USB EHCI Controller (prog-if 20)
    Subsystem: Hewlett-Packard Company Device 30e4
    Flags: bus master, 66MHz, medium devsel, latency 64, IRQ 11
    Memory at 54309500 (32-bit, non-prefetchable) [size=256]
    Capabilities: [c0] Power Management version 2
    Capabilities: [e4] Debug port: BAR=1 offset=00e0
    Kernel driver in use: ehci_hcd

00:13.0 USB Controller: ATI Technologies Inc SB700/SB800 USB OHCI0 Controller (prog-if 10)
    Subsystem: Hewlett-Packard Company Device 30e4
    Flags: bus master, 66MHz, medium devsel, latency 64, IRQ 11
    Memory at 54306000 (32-bit, non-prefetchable) [size=4K]
    Kernel driver in use: ohci_hcd

00:13.1 USB Controller: ATI Technologies Inc SB700 USB OHCI1 Controller (prog-if 10)
    Subsystem: Hewlett-Packard Company Device 30e4
    Flags: bus master, 66MHz, medium devsel, latency 64, IRQ 11
    Memory at 54305000 (32-bit, non-prefetchable) [size=4K]
    Kernel driver in use: ohci_hcd

00:13.2 USB Controller: ATI Technologies Inc SB700/SB800 USB EHCI Controller (prog-if 20)
    Subsystem: Hewlett-Packard Company Device 30e4
    Flags: bus master, 66MHz, medium devsel, latency 64, IRQ 11
    Memory at 54309400 (32-bit, non-prefetchable) [size=256]
    Capabilities: [c0] Power Management version 2
    Capabilities: [e4] Debug port: BAR=1 offset=00e0
    Kernel driver in use: ehci_hcd

00:14.0 SMBus: ATI Technologies Inc SBx00 SMBus Controller (rev 3a)
    Subsystem: Hewlett-Packard Company Device 30e4
    Flags: 66MHz, medium devsel
    Capabilities: [b0] HyperTransport: MSI Mapping Enable- Fixed+
    Kernel driver in use: piix4_smbus
    Kernel modules: i2c-piix4

00:14.2 Audio device: ATI Technologies Inc SBx00 Azalia (Intel HDA)
    Subsystem: Hewlett-Packard Company Device 30e4
    Flags: bus master, slow devsel, latency 64, IRQ 10
    Memory at 54300000 (64-bit, non-prefetchable) [size=16K]
    Capabilities: [50] Power Management version 2
    Kernel driver in use: HDA Intel
    Kernel modules: snd-hda-intel

00:14.3 ISA bridge: ATI Technologies Inc SB700/SB800 LPC host controller
    Subsystem: ATI Technologies Inc SB700/SB800 LPC host controller
    Flags: bus master, 66MHz, medium devsel, latency 0

00:14.4 PCI bridge: ATI Technologies Inc SBx00 PCI to PCI Bridge (prog-if 01)
    Flags: bus master, 66MHz, medium devsel, latency 64
    Bus: primary=00, secondary=80, subordinate=8f, sec-latency=64
    I/O behind bridge: 00001000-00001fff

00:14.5 USB Controller: ATI Technologies Inc SB700/SB800 USB OHCI2 Controller (prog-if 10)
    Subsystem: Hewlett-Packard Company Device 30e4
    Flags: bus master, 66MHz, medium devsel, latency 64, IRQ 11
    Memory at 54304000 (32-bit, non-prefetchable) [size=4K]
    Kernel driver in use: ohci_hcd

00:18.0 Host bridge: Advanced Micro Devices [AMD] Family 11h HyperTransport Configuration (rev 40)
    Flags: fast devsel
    Capabilities: [80] HyperTransport: Host or Secondary Interface

00:18.1 Host bridge: Advanced Micro Devices [AMD] Family 11h Address Map
    Flags: fast devsel

00:18.2 Host bridge: Advanced Micro Devices [AMD] Family 11h DRAM Controller
    Flags: fast devsel

00:18.3 Host bridge: Advanced Micro Devices [AMD] Family 11h Miscellaneous Control
    Flags: fast devsel

00:18.4 Host bridge: Advanced Micro Devices [AMD] Family 11h Link Control
    Flags: fast devsel

01:05.0 VGA compatible controller: ATI Technologies Inc RS780M/RS780MN [Radeon HD 3200 Graphics]
    Subsystem: Hewlett-Packard Company Device 30e4
    Flags: bus master, fast devsel, latency 0, IRQ 2300
    Memory at 40000000 (32-bit, prefetchable) [size=256M]
    I/O ports at 5000 [size=256]
    Memory at 54200000 (32-bit, non-prefetchable) [size=64K]
    Memory at 54100000 (32-bit, non-prefetchable) [size=1M]
    Capabilities: [50] Power Management version 3
    Capabilities: [a0] Message Signalled Interrupts: Mask- 64bit+ Queue=0/0 Enable+
    Kernel driver in use: fglrx_pci
    Kernel modules: fglrx

02:00.0 Ethernet controller: Marvell Technology Group Ltd. Device 4357 (rev 10)
    Subsystem: Hewlett-Packard Company Device 30e4
    Flags: bus master, fast devsel, latency 0, IRQ 2301
    Memory at 53000000 (64-bit, non-prefetchable) [size=16K]
    I/O ports at 3000 [size=256]
    Capabilities: [48] Power Management version 3
    Capabilities: [5c] Message Signalled Interrupts: Mask- 64bit+ Queue=0/0 Enable+
    Capabilities: [c0] Express Legacy Endpoint, MSI 00
    Capabilities: [100] Advanced Error Reporting <?>
    Capabilities: [130] Device Serial Number 00-24-81-ff-ff-62-99-aa
    Kernel driver in use: sky2
    Kernel modules: sky2

"ATI Technologies Inc SBx00 Azalia (Intel HDA)"をキーワードに検索すると,

解決に直接結びつかない記事ですが,
こんな日本語記事をみつけました.

> Written on 2009 年 3 月 15 日
> "メモリー容量の壁は 4GB ＠ Intel HDA ドライバー (alsa-driver)"
> http://www.chanel.ath.cx/ja/?p=21
>
> [追記 22:45 翻訳挿入 3/16 03:04]
> * Daniel Koukola さんが，私の間違いだと訂正を入れてきました．これは， AMD/ATI SB600 のバグだそうです．

英語のサイトでも報告は多数あるみたいです.
RHELサポートフォーラムにも約１年前の投稿が見つかりましたが,
解決しましたみたいなことは載ってません…


Ubuntuフォーラム内でも,１年前に質問があった様です.

> インデックス » 初心者サポート » オーディオなどの音が出ない
> https://forums.ubuntulinux.jp/viewtopic.php?pid=8890

の,最後の "#4" に書かれているので見落としされているかも知れません.

主メモリ容量と関係があるみたいなので,
カーネル側でも該当デバイス対応の変更が入る必要が出ているのかも知れません.
海外でも報告は上がっているみたいなので, 対応待ちなのかと…

突然使えなくなった方のほうは,もしかして主メモリ増設してませんか？



あ,でも,ヘッドホン出力は出ているんですよね？
だったら, "音量調節ツール"の, "Speaker"がミュートされてるだけかも知れませんね.

>youreさま、hmatsueさま
解決しました。
windowsとubuntuのデュアルブートにしているのですが、windows側でミュートにしていたからだと思われます。
情報提供いただきましてありがとうございました。