Could be that or could be a faulty memory module which caused exactly that problem on my wife's PC recently. Have you one module or two, if two - take one out and alternate - also download mem test click here. Also
Right-click My Computer, and then click Properties.
Click the Advanced tab.
Under Startup and Recovery, click Settings to open the Startup and Recovery dialog box.
Clear the Automatically restart check box, and click OK the necessary number of times.
Restart your computer for the settings to take effect.
Now a reboot and a fatal error occurs, you'll at least see it and it won't cause an automatic reboot. You still have to sort out what's causing the problem - post any message back for help.