"Easy Windows XP Troubleshooting" Initial suggestion is simply to switch PC off and on a few times or even leave it alone overnight to give the OS a chance to sort itself out. If PC cannot boot into Safe mode then the next most constructive option is to boot from an XP installation disc in CD-Rom drive.
Switch on, insert XP disc and wait. If you have the essentials and the PC does boot from ROM then press R for recovery console.
According to the author this seems to be the last best hope for your computer.