The system is crashing for some reason, either hardware or software.
You should get a blue screen whith the name of the crash type, a group of
codes which all begin with 0x... and perhaps the name of a driver filename
ending in .sys.
By default this screen disappears quite quickly and the system restarts.
go into
control panel/system/advanced/startup and recovery settings
Untick, "Automatically Restart"
Post the information I mentioned above when you get the blue screen.
Windows xp also records this information in the system eventlog, but
unfortunately does not record the name of the driver for driver related
crashes. You have to get that from the blue screen
Go into the system event log
start/run
eventvwr.msc
click on system in left pane.
Look down the events in the right hand pane and look for events labelled
either "save dump" or "System error"
Double click on the latest and use the copy button below the 2 arrow keys to
copy the error information, and then use right click/paste to paste it into
you reply post.
Paul