no active mixer device

hello to all.
I have my next door neighbors computer here in my room because I might buy it off of him but he told me his cousin reformatted it and now when I turn it on I have no volume control and no option for any sound! It tells me NO ACTIVE MIXER DEVICE and SO ON! Someone help me please. I read a couple of posts from NOO-NOO & I got my computer report from EVEREST so here goes:

Computer:
Operating System Microsoft Windows XP Professional
OS Service Pack -
DirectX 4.08.01.0810 (DirectX 8.1)
Computer Name TRANS
User Name Usuario

Motherboard:
CPU Type Mobile AMD Athlon XP, 1350 MHz (13.5 x 100)
Motherboard Name PCChips M863G (2 PCI, 1 AGP, 1 CNR, 2 DDR DIMM, Audio, Video, LAN)
Motherboard Chipset SiS 741GX
System Memory 512 MB (DDR SDRAM)
BIOS Type AMI (01/15/04)
Communication Port Communications Port (COM1)

Display:
Video Adapter NVIDIA GeForce2 MX 200 (Gateway) (32 MB)
3D Accelerator nVIDIA GeForce2 MX 100/200
Monitor Compaq Presario MV500 [15" CRT] (843BF48OS931)

Multimedia:
Audio Adapter SiS 7012 Audio Device

Storage:
IDE Controller SiS PCI IDE Controller
Floppy Drive Floppy disk drive
Disk Drive WDC WD800BB-00JHC0 (74 GB, IDE)
Optical Drive HL-DT-ST RW/DVD GCC-4522B
SMART Hard Disks Status OK

Partitions:
C: (NTFS) 76308 MB (72397 MB free)

Input:
Keyboard PS/2 Millennium Keyboard
Mouse Microsoft PS/2 Mouse

Network:
Network Adapter SiS 900 PCI Fast Ethernet Adapter (192.168.1.96)

Peripherals:
USB1 Controller SiS 7001 PCI-USB Open Host Controller
USB1 Controller SiS 7001 PCI-USB Open Host Controller
USB2 Controller SiS 7002 USB 2.0 Enhanced Host Controller

please help me get the sound back!!
:)