Different BSODs cannot find the problem

Hello,

I need help figuring out the problem here.
It started out of the sudden while playing and never got over it since then.

I can't even tell if it's an hardware or software problem because for my mainboard and also for my w-lan card no proper Win7 drivers exist. But I have never had such problems before.
The fact that bluescreens even appeared on a fresh windows install (without installing anything else manually) probably points to a hardware problem?

Everything I've tried:
Different RAM and slots
New Power Supply
New HDD (Sata now and before)
BIOS Update

The BSOD appears within 2minutes of starting the machine.
Running programs like memtest,furmark,prime95 or just blender with a really big scene prevent the BSOD and let me freely operate the machine meanwhile. Soon after closing these programs a BSOD appears.

MemTest gives alot of errors, Prime (CPU&RAM) doesn't give a single one.

While using this workaround I loose connection to the router randomly when downloading stuff (sometimes when loading a page, alot oftener when loading bigger files for > 5 minutes) just like the wireless card restarted.
Regularly when playing soundfiles (web&hdd) from videos or programs there is a delay of exactly 6seconds each time until the sound is played. (It synchronizes with video after).

Maybe someone here can help me to figure out the problem.

I cannot install bigger windows-updates because while installing them memtest cannot be executed.