Does it give you any error message or such? Look in Event Viewer
[eventvwr.msc] in the system and application logs to see if anything there
has been recorded that might be helpful. Try booting into Safe Mode to see
if it still happens. If it does not then most likely you have a problem with
malware or severe software/driver conflict. If it still happens you may have
a hardware problem such as a bad power supply or overheating CPU which can
easily be caused by a clogged CPU fan/heatsink or failed CPU fan.
Assuming it is malware make sure that you are scanning your computer with a
antivirus program that is using the latest virus definitions downloaded from
the vendors website. Since it is rebooting you may have to run your virus
scan in Safe Mode at least to start. If you can at least identify the virus
from a virus scan but the antivirus program can not seem to remove it search
Google or SARC for the name of the virus for specific removal instructions
that may include a special tool that you need to download. The links below
may help including one to McAfee Stinger which is a compact tool you can run
to check for and remove some of the most common malware and tips on how to
secure your PC to minimize the possibility of future problems. --- Steve
http://securityresponse.symantec.com/ --- SARC from Symantec
http://vil.nai.com/vil/stinger/ -- McAfee Stinger tool
http://www.trendmicro.com/download/dcs.asp --- Trend Micro Sysclean
http://www.trendmicro.com/download/pattern.asp --- Sysclean pattern file in
..zip format
http://www.microsoft.com/athome/security/protect/windows2000/default.mspx ---
Protect your PC for Windows 2000
