Hola de nuevo.
En primer lugar, gracias a los dos. Imagino que el problema acabará siendo una auténtica tontería, pero es lo que tenemos los principiantes; no somos capaces de ver la solución ante nuestras narices...
Introduzco los comandos de Alfonskunk y sale esto:
~$ aplay -l
aplay: device_list:252: no se encontraron tarjetas de sonido...
sergi@Nube:~$ lspci -v
00:00.0 Host bridge: Intel Corporation 82845G/GL[Brookdale-G]/GE/PE DRAM Controller/Host-Hub Interface (rev 02)
Subsystem: Intel Corporation 82845G/GL[Brookdale-G]/GE/PE DRAM Controller/Host-Hub Interface
Flags: bus master, fast devsel, latency 0
Memory at e8000000 (32-bit, prefetchable) [size=64M]
Capabilities: <access denied>
Kernel driver in use: agpgart-intel
00:01.0 PCI bridge: Intel Corporation 82845G/GL[Brookdale-G]/GE/PE Host-to-AGP Bridge (rev 02) (prog-if 00 [Normal decode])
Flags: bus master, 66MHz, fast devsel, latency 64
Bus: primary=00, secondary=01, subordinate=01, sec-latency=32
Memory behind bridge: ec000000-edffffff
Prefetchable memory behind bridge: e0000000-e7ffffff
Kernel modules: shpchp
00:1d.0 USB controller: Intel Corporation 82801DB/DBL/DBM (ICH4/ICH4-L/ICH4-M) USB UHCI Controller #1 (rev 02) (prog-if 00 [UHCI])
Subsystem: Intel Corporation Latitude X300
Flags: bus master, medium devsel, latency 0, IRQ 16
I/O ports at d800
Kernel driver in use: uhci_hcd
00:1d.1 USB controller: Intel Corporation 82801DB/DBL/DBM (ICH4/ICH4-L/ICH4-M) USB UHCI Controller #2 (rev 02) (prog-if 00 [UHCI])
Subsystem: Intel Corporation Latitude X300
Flags: bus master, medium devsel, latency 0, IRQ 19
I/O ports at d000
Kernel driver in use: uhci_hcd
00:1d.2 USB controller: Intel Corporation 82801DB/DBL/DBM (ICH4/ICH4-L/ICH4-M) USB UHCI Controller #3 (rev 02) (prog-if 00 [UHCI])
Subsystem: Intel Corporation Latitude X300
Flags: bus master, medium devsel, latency 0, IRQ 18
I/O ports at d400
Kernel driver in use: uhci_hcd
00:1d.7 USB controller: Intel Corporation 82801DB/DBM (ICH4/ICH4-M) USB2 EHCI Controller (rev 02) (prog-if 20 [EHCI])
Subsystem: Intel Corporation 82801DB/DBM (ICH4/ICH4-M) USB2 EHCI Controller
Flags: bus master, medium devsel, latency 0, IRQ 23
Memory at ee100000 (32-bit, non-prefetchable) [size=1K]
Capabilities: <access denied>
Kernel driver in use: ehci_hcd
00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev 82) (prog-if 00 [Normal decode])
Flags: bus master, fast devsel, latency 0
Bus: primary=00, secondary=02, subordinate=02, sec-latency=32
I/O behind bridge: 0000c000-0000cfff
Memory behind bridge: ee000000-ee0fffff
Prefetchable memory behind bridge: 40000000-400fffff
Kernel modules: shpchp
00:1f.0 ISA bridge: Intel Corporation 82801DB/DBL (ICH4/ICH4-L) LPC Interface Bridge (rev 02)
Flags: bus master, medium devsel, latency 0
Kernel modules: iTCO_wdt, intel-rng
00:1f.1 IDE interface: Intel Corporation 82801DB (ICH4) IDE Controller (rev 02) (prog-if 8a [Master SecP PriP])
Subsystem: Intel Corporation Device 24c2
Flags: bus master, medium devsel, latency 0, IRQ 18
I/O ports at 01f0
I/O ports at 03f4
I/O ports at 0170
I/O ports at 0374
I/O ports at f000
Memory at 40100000 (32-bit, non-prefetchable) [size=1K]
Kernel driver in use: ata_piix
00:1f.3 SMBus: Intel Corporation 82801DB/DBL/DBM (ICH4/ICH4-L/ICH4-M) SMBus Controller (rev 02)
Subsystem: Intel Corporation Device 24c2
Flags: medium devsel, IRQ 11
I/O ports at 0500
Kernel modules: i2c-i801
01:00.0 VGA compatible controller: NVIDIA Corporation NV34 [GeForce FX 5200] (rev a1) (prog-if 00 [VGA controller])
Flags: bus master, 66MHz, medium devsel, latency 248, IRQ 16
Memory at ec000000 (32-bit, non-prefetchable) [size=16M]
Memory at e0000000 (32-bit, prefetchable) [size=128M]
[virtual] Expansion ROM at ed000000 [disabled] [size=128K]
Capabilities: <access denied>
Kernel driver in use: nvidia
Kernel modules: nvidia_173, nvidia_173_updates, nouveau, nvidiafb
02:01.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL-8139/8139C/8139C+ (rev 10)
Subsystem: Realtek Semiconductor Co., Ltd. RTL-8139/8139C/8139C+
Flags: bus master, medium devsel, latency 32, IRQ 17
I/O ports at c000
Memory at ee010000 (32-bit, non-prefetchable)
[virtual] Expansion ROM at 40000000 [disabled] [size=64K]
Capabilities: <access denied>
Kernel driver in use: 8139too
Kernel modules: 8139too, 8139cp
02:05.0 Multimedia audio controller: Creative Labs SB0400 Audigy2 Value
Subsystem: Creative Labs Device 4002
Flags: medium devsel, IRQ 21
I/O ports at c400
Capabilities: <access denied>
Kernel modules: snd-emu10k1
Os garantizo que la tarjeta de sonido está insertada en la placa y conectada. De hecho, un rato antes de formatear windows e instalar ubuntu estaba trabajando con ella.