Unfortunately that's a bit messy to deal with. :-/
Odds are the system is faulting and dropping into an automatic restart,
followed by a fault that triggers another restart, etc. The problem is that
unless you can see the fault message it's virtually impossible to determine
if you're having a hardware or driver/service problem.
You can try this
http://support.microsoft.com/default.aspx?scid=kb;en-us;307545&Product=winxp
to see if you can get to a functioning restore point.
You can also attempt to isolate the problem in place via recovery console.
That's dicey, even for some one that is technically competent. See
http://support.microsoft.com/default.aspx?kbid=244905 for an explanation of
how to disable startup items/services via recovery console. About midway
down this article
http://support.microsoft.com/default.aspx?scid=kb;en-us;316434&Product=winxp
is a list of most of the services that the OS uses in a default
configuration. Anything *not* on the list should be safe to disable for
diagnostic purposes. RPC is the *only* service that must be left on. All the
over services may, temporarily, be disabled but avoid disabling anything
that is shown by default as automatically started. Although it's possible to
get by with disabling some of those, disabling them blindly can cause worse
problems than you currently have.
Alternatively, you can try a repair reinstall. The disadvantage is that if
certain parts of the registry are damaged, especially related to the system
hive, a repair reinstall might not work. You can also try a parallel install
so that you can trouble shoot the damaged OS using something other than
recovery console, but unless you have a separate drive/partition, a parallel
install will stomp on part of the existing OS instance.
--
Walter Clayton - MS MVP(WinXP)
Associate Expert
http://www.microsoft.com/windowsxp/expertzone
Any technology distinguishable from magic is insufficiently advanced.
http://www.dts-l.org
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