Try booting into Safe Mode (press F8 ) & see if u get the same problem. If not, then it is likely a software related problem.
Here use “msconfig” to disable all startup programs and turn them on one by one until the problem returns. Also check power setting to see if this could be related to an attempt to go into sleep mode….
U can check memory using the built-in memory tester with Windows 7 by Start > memory diagnostics
Also see the Event Viewer !