There are so many answers to this loop de loop that depend on exactly where
it is looping.
More details would be helpful....but
the fix all cure almost all solution would be to do a repair install if it
was an XP problem. http://www.michaelstevenstech.com/XPrepairinstall.htm
if its a hardware problem(before XP takes over) check your BIOS settings and
connections inside your system.
peter