Sound And Product Key Not Working.

so after finally getting a massive virus off of my sister's computer i've had to re-install everything, msn, anti-virus stuff etc. but now i have two problems that i can't seem to find the answer for anywhere! first, windows (xp home edition) keeps asking me to activate it everytime i log on, i click on the bubble and follow the steps, i go onto "activate through the internet" and then "no don't register just get activated", i put in the product key that's on the side of her desktop and it says it's invalid, so i tried a keyfinder and it came up with a different one, so i entered that in instead and that didn't work either. it may be relevant to mention that the operating system cd might be from my parent's laptop or my sister's computer, i could only find one so i used that. any help on this would be greatly appreciated.

secondly the sound card driver isnt working i don't think. the log on music works but there's no icon on the bottom of the screen with the picture of a speaker. i go on the internet and click a random Internet video and that doesn't have any sound. there's nothing wrong with the speakers (because i unplugged them and put them into my laptop and they work fine).