Friends bought an old computer from some guy going into the army.
Worked fine until they connected a small WalMart home theater system to it. It's about 50watts, nothing special, and can be connected to a computer/cd player via headphone jack connection. Sound died. Everythign else works, just no sound. We tried via the CD drive jack, the motherboard and the installed sound card. Nothing. So I removed the sound card and tried on the motherboard. nothing. I'm not too tech-savvy when it comes to sound. I just expect it to work when I pay $200 for my motherboards and am not used to 4-year old+ motherboards sporting an AGP slot (yes, agp is ancient to me).
I'm thinking when they plugged it in, it ruined the sound card drivers. but until I'm sure of the problem and ruling out a fried motherboard sound controller, I don't want to uninstall software.

Cliffnotes:
working computer --> plug in 50watt walmart speaker system --> sound no worky
removed sound card, onboard sound doesn't work
checked all windows settings, muting off, sound on high, everything seems set.

Any help?

tried different speakers (headphones)?

Just pluging in a pair of speakers shouldn't mess up the sound drivers, what might have happened is some sort of static discharge ruined the soundcard, but in that case the onboard sound should work. Sometimes onboard devices need the correct drivers installed too, did you have those installed?

Do you mean that the computer sound is working fine when it was purchased from the previous owner? If that is the case that you don't receive any sound on your speaker, change to another speaker to test it. It could be that the speaker or earpiece that you are using is faulty, like what Blacklaser commented.

Otherwise, make sure that the drivers are installed correctly, matching your sound card hardware. a wrong driver installed will only let Windows know that a physical sound card is present but will not function properly.

If you are trying on the earpiece output jack on your CD-ROM, it could be that the direct sound output from the CD-ROM is not properly connected in the motherboard. There should be a direct wire connecting the CD-ROM straight to the sound card, which then will process and output the sound directly to your earpiece through the jack on the CD-ROM.

Yeah I forgot that, that is very important otherwise only audi CDs in the drive will play on that jack.

try gettin a new sounds card and see if it was just the sound card

maybe 20 bucks will get u a new one

tried different speakers/headphones, the works. I might drop $20 for a sound card but the computer's worth less than a new sound card as it is. I'll try downloading the drivers but last time i checked, the sound card didn't have any label or engraving on it so i may have to pop the HS and take a look at the core. (*sigh*) so much work for such a worthless PC. what friends will do, i guess, thanks guys