Sounds like a microsoft problem to me!!! get yourself into safe mode, backup all your data on dvd or if you have an external hard drive, run the files and settings transfer, which can be done in dos and perform a clean install of xp onto your system, another idea is to purchase a program called ‘‘system mechanic 6.0’’ it luckily runs in safemode, may also find a start up / registry error in the boot defrag process, i’ve had the same problem on several pc’s that ive fixed in the past, no need to worry as of yet, by any chance, have you installed any kind of program such as ‘‘windows blinds’’ or style xp? these can also mess up your system, deleting crucial files and replacing them ui with coding that is not fully compatible with xp 8)