pc wont boot up

[Reapers]

hmm this is a tricky issue
usually requires the cd to fix

could try 2 things

your master boot record could be corrupt or damaged

burn this iso to a disc

http://www.thecomputerparamedic.com/files/rc.iso

it will act like xp install disc but will only offer the recovery console
then just follow this xp tutorial on fixing the mbr
How to fix MBR in Windows XP and Vista


also try to access system restore through command line
if first suggestion does not work

(scroll down to more information to see how)
How to start the System Restore tool by using the safe mode option with the Command prompt in Windows XP

[Bann32]

Put the folllowing in notepad -

Shutdown /a /t 3153600

In the save give it a name like "stop.bat" (including the quotes)
and the file type is all types.


That should stop the shutdown then you can get rid of the problem causing it. A virus scan and scan disc would be a good start.