Stop my Netbook from shutdown automatically

Hello, I have a netbook and recently it keeps shutting down on me by itself. It shown the system shutdown box with 60 sec. And the reason for the shutdown is the services.exe I was able to stop the shutdown by using the command shutdown -a. But it just keeps on happening later on at random time. I just can't open event viewer, services, or My Compter's Properties after it happened. I scanned it with spybot and superantispyware, but found nothing. Any idea what's the reason? thanks in advance.

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