@mello
Boot the PC, if it won?t boot into XP as normal boot into safe mode (F8), right click on My Computer, select Properties, select the Advanced Tab, under Start-up and Recovery click Settings, and under System Failure untick the box Automatic Restart, reboot and see if that cures the problem
If you?re hard drive C has less than 1.5Mb of space then that could be the problem because XP needs that much space to use as a swap file (It loads programs and Data there to run faster)
Brian