Windows XP constant reboot

[stephen]

I have Windows XP Home SP3

I did a repair install from a Windows XP Home SP2 CD

The PC now cannot boot

Windows XP starts to load then it drops to Checking File System C:

the Checking says it is finished then just reboots straight after.

I have booted to recovery Console on the XP CD
and ran these commands none of them fixed the problem
chkdsk c: /p

fixboot c:
fixmbr c:

This did not fix the problem.