Perhaps a solution to ur problem
I've been using windows xp for about a year(since the time i bought my new pc) and i got something like the problem you have some days ago. after the xp boot screen windows would not load. i formatted but it did not resolve the problem.
I would consider that you have a problem with your boot partition. Boot your pc in DOS from a startup disk or your bootable me installlation cd. then run fdisk and erase your primary boot partition. Reboot and run fdisk again. Create a new primary partition. Set it as active partition and exit fdisk. format this new partition (Should be the same drive letter it was initially) and run windows setup again.
If you run xp setup i recommend you convert your created fat32 drive(above) to ntfs. :D :D ;)