You probably deleted some critical file. if you can't get it to repair......
reformat
try hitting f3 when booting from the xp cd.
I forgot the options that you have to type here, but if you start typing anything it will tell you the options
Can you press F8 as soon as POST test finishes & select safe mode with command prompt? If so, try running chkdsk from there instead of using boot disk/CD.