Windows 7 - PC freezes at startup or randomly black screen

Hi,

some weeks ago I built a PC for my brother but it still isn't working correctly.
The first motherboard was damaged as it destroyed the RAM, means the first check with Memtest86 always showed no errors but when checking after a while (1-2 days) the RAM was full of errors. Well, motherboard is changed now, new RAM, both has no more errors but it still fails.

Most of the time the system doesn't start, it freezes during the "starting windows" screen. And as it seems always at the same position as there is always 1 "dot" behind the "starting windows" and my brother told me when the keyboard lights up he knows that the system will boot.
But even after that the system will quit with a black screen after a short time.

Here is the system information:

CPU: AMD Phenom II X2 555 3.20GHz BE
Mainboard: Asus M4A89GTD PRO/USB3
RAM: GEIL 4 GB DDR3-RAM PC1333 CL7 2x2GB KIT2
HDD: 2*1000GB Western Digital Caviar Green WD10EARS
PSU: 650W Super Flower SF650P14P Black
OS: Windows 7 64bit but not sure about the version


A discrete graphic card isn't build in at this moment. The CPU is not overclocked.
I looked for minidump files but (1) it is hard to boot into windows and (2) there were none, perhaps the last wipe wasn't too long ago. Does windows create minidumps when it freezes at startup?
Booting in safe mode with boot log & OS boot information resulted in a freeze/black screen after all files are loaded and it says that windows will boot now.

Sorry for my english and thanks for your help.