Windows 7: System shutting down during logon

I have been having problems during logon that I get system shutdown message while typing in password, sometimes before. I eventually get in after several attempts. This also happens in safe mode. What could be causing this behavior?

For testing open a new account and see if problem continues. It could be a corrupted account.

Thanks for the suggestion and I have done that. I will now wait to see what happens.

Did you do this?
SFC /SCANNOW Command - System File Checker

Thanks for the suggestion. I just did the SFC /scannow command and all OK.
Thanks

Does happen in safe mode, may not be software.

Run for 8 scans overnight. Report results
Download memtest86 and test RAM
www.sevenforums.com/tutorials/105647-ram-test-memtest86.html

A long shot but try this
Tools
Internet options
advanced
Reset
Resets IE8

OK, I have just downloaded the MEMTEST and will give that a shot when I get a chance, Thanks

Just for kicks try the IE8 reset.

How do I Reset IE8?

As above post