Windows 7: Blank screen at boot up

Hi.

Yesterday I recognized, that my screen was blank at start up.



I rebooted in safemode, and then the screen was ok.

There I restored the computer to an earlier state, and it ran ok after

The same ocured this morning, and now I don't have the opportunity to
restore as there is no restore point.

What I did when the computer ran ok was that I started up NFS.
No more.

What could be wrong here ?

Now after a little over 2 hours the screen waked up again.

The screen was not black, but silver.

The graphics card is a NVIDIA, where I have the VGA connected to one monitor, and
via a DVI to VGA adapter another monitor is connected.

I have encountered, that something is slow, and I have seen it a while.

The DPC is ok, and also the CPU load measured with Process Explorer.

I have defragged the computer, and yes, I have ran all what O could get aware of
to have a clean computer.

BUT I might have overseen something.

CAN it be the Grapichs Card ?