Windows 7 - Crashing for (probably) no reason

Hey.

I have got a real problem.
Since monday, I have not used my computer since last thursday (16-19.06.2011), I get constantly crashes with my computer.

I have already reinstalled Win 7 Prof 64bit.

But it did not change anything.

I also downgraded my computer to 2gb ram... it did not help.
The picture freezes without any reason. I was only surfing the internet, nothing more - with my fresh reinstalled windows...

I thought it was the analogue output of my graphiccard, because here, at my parents' house it worked for the last two days, without the reinstalling...
But after reinstalling Windows 7, the computer crashed down again for (probably) no reason...

I do not get it, and I hope for your help,
best regards from Germany,

Sebastian

Might want to test that remaining ram.
RAM - Test with Memtest86+
Let it run overnight (it runs independent of windows)
If memtest itself freezes you have a hardware problem for sure.

I tested the RAM-units seperatly on slot 1.
Unit one showed the following failure: picture
The others were okay.

Then I put the units back together, but unit one on slot 4 and tested again - no failure occured.

After restarting the computer, it freezed after logging in...

Btw: the computer runs perfectly in "safe mode" (hopefully it's the right word for running a computer only with the most important drivers).
AND: it is not really crashing - more freezing...

uninstall windows media software, player, movie maker...and so on. also disable themes on the desktop

Did not help