just perform all the routine stuff ...

scan with latest virus definitions

if possible do an online scan

run spybot nd adaware

run > msconfig > clear all unwanted entries

remove CD ROM/DVD ROM drives frm device manager,restart the PC,XP will install back the devices nd check....
still not working ??? check out ur SMPS...can be its fault...as soon as CD/DVD drive draws power the system shuts down...try out this way...disable autorun..insert the disc nd restart i.e the system shud start with a disc already in the drive... open my computer after restart nd browse the CD...see if system shuts down ..