Haven't given us much to go on there, but check the basics first:
Are you running on batteries? Perhaps the battery is not holding much charge
any more and the shutdown is automatic low battery shutdown.
Do you have a power scheme enabled that shutsdown after 10 minutes and it
triggering it?
Do you have any rogue processes running in the task manager? Make sure your
virus software is up-to-date, then do a full virus scan. Do a spyware scan.
There will probably be other replies here about more technical matters such
as heat and failing components, but tackle every possibility, starting with
the easiest.