When i rebooted my computer this morning, it didn't fully load, just after the welcome screen it stops loading, no desktop or taskbar, alt ctrl del works,and i tried logging in with different users, same problem. So i tried in safe mode, but it like keeps refreshing, the warning box will keep poping up, i got it stop doing that in another user, but when i click start and click programs, it refreshes popup appears I tried system restore, it didn't change anything. I put XP CD in, and now it doesn't recognise my CD key Whats wrong how can i fix it?

Try rebooting with the CD and reformat the drive. Sorry. Before you do that, if you can, some how backup your existing files that you want to save.

did you try using the repair consol? with the xp cd in? like typing chkdsk /p? if you didnt try this it may help, other ways you must reinstall xp. i hope you have all your data baked up 1.turn off your computer 2.turn it back on. 3.insert your xp cd. 4.if you have your bios set up to boot from cd, first youll get a note telling you: "to boot from cd hit any key". if you dont have your puter set up to boot from cd first you must go into the bios and change the boot sequence, i hope you know how to do that. 5.after the xp cd loads and you get to the welcome screen, hit the "R" KEY for repair then you probably have to choose what installation you want to fix and your administrator password, do all that. 6.on the command prompt, type: chkdsk /p. this will take a while. 7.after the repair is finish type on the commnd prompt : fixboot type ok or yes to the following questions .this should take 5 seconds. 8.on the command prompt type "exit" if everything went right youll be able to reboot ok, if not, reinstall xp. cheers and good luck let us know what happened.

Maybe this: Computer Seems to Stop Responding Before the Desktop Is Displayed http://support.microsoft.com/default.aspx?scid=kb;en-us;320560