Re: No sound?
Right clic My Computer>Properties>Hardware>Device Manager> click on the + beside the sound, video and game controller. If you have a yellow exclamation mark, it means you have a conflict. Right click on the device which has a conflict and then properties>drivers update driver. Windows will seach for the drivers a re'install them.
From what you wrote, your brother was playing a game and listening to music at the same time!! which sound leads? Can you play two games at the same time! Well you can't listen to two different sound source at the same time.
You can also check in your control panel to make sure your sounds have been assigned to the right device, in case you have 2; like a sound card and another one on your mobo.
Asus P4P800 SE
Intel P4 3.2 Gig 1024 Meg PC3200 cas latency 2.5
RAID 0 2-36.7 Gig SATA WD 10,000 RPM
200 Gig WD ATI ALL-IN-WONDER 9600XT
6500 Kb bandwith Internet Connection