Re: Windows xp will NOT start
You can first try re-activation (tell them your old motherboard went out, it's not impossible, my old Compaq motherboard went out just recently, but it ran Win2K so I didn't have to activate). If that works, good, otherwise...
A) Buy a new (preferably non-OEM) copy of WinXP (Newegg sells it, so do a lot of stores). It will have a good activation number.
B) Use Linux. If all you use your PC for is Web browsing, e-mail, watching online videos, and listening to music, Ubuntu can do all of that and is entirely (and legally) free to use on as many computers as you want. You can dual-boot Ubuntu (for Web stuff) and WinME (for Windows stuff) together if you want.
C) Upgrade to Vista. The comp might be able to, but the question is, do you really want to go with an unstable OS that suffers from horrible compatibility?
I'd stick with XP if I were you.