Boot problem... plz hlp

I'm having problem whit my computer I cant start it. It worked just fine before just a little slow so I thought It needs to be rebooted so I did that but now i will not start... I come as far as to the Win XP loading screen then I get a blue screen for about 0.001 sec and then i reboot itself...  

I cant formate it either...   When i try I get a massage "cant load command.com"  why?? why?? plz help...

                                                                  //RunNer

Boot from the XP CD (go into BIOS and set the CD as first boot device, put your XP system CD in the drive, and reboot) and re-install XP with 'repair' option to fix corrupted files.

Yeah, but first think about this...
Do you have backups of your files somewhere?