Win7 KSOD after reboot. No recovery possible!?

Hi.
Two days ago my compi got very unresponsive so I rebooted it.
I have a 4 year old Dell studio XPS 7100 running win7 (x64).
After the reboot I noticed that the startup screen was different i.e. was very low graphics quality, the 4 colored windows icon did not appear. It only displays a white bar filling and says windows is starting but the time this takes seems a bit too fast to look proper IMHO. After the boot i end up on a black screen with only the mouse cursor visible. I can move it around but nothing else works (no right-click or taskmanager). After searching dozens of forums to fix this I am at a loss. Here is what I have tried so far.

System-repair: I can access the win7 repair screen via F8. However, starting windows in safe mode as well as trying to use the repair option results in the KSOD. Putting the VGA to low resolution did not help either.

Recovery-CD: I got a Win7 x64 recovery CD and it boots alright but after the boot the windows screen doesnt appear. instead i get the KSOD again . Btw i did not forget to switch boot devices in the BIOS Just for fun, I unplugged the HD from the computer and surprisingly, this made the boot-CD go into the welcome screen. However this is obviously not the solution I am looking for this I'd have no HD to do a clean install.

Dell utilities: I ran several tests from the dell utility symptom tree and as well as the pre-configured tests but it didnt return any errors.

CMOS: I've read in some forums that malware can affect the CMOS so i tried to re-boot it by removing the battery for a fewminutes. I am not sure if this has done anything.

Antivirus: I have tried to find any malware by running windows defender offline from a USB stick. However, after it boot from the stick, I get a black screen and after a while it displays an error message that i cannot read properly because it disappears immediately and the computer reboots. It looks like this message contains a frowning smiley and says stl "your computer cannot ......". I tried both the 32 and 64 ver of the defender but it seems i am stuck here too.

Graphics: I upgraded my graphics card a few months ago so i was able to put the old one back in but after reboot I retrieve the same result. Some forums suggest the KSOD to be from HDMI cables but I am using a plug with pins (pardon my ignorance I forgot how these are called ). So this doesnt seem to be the problem either.

At the moment I like to believe that some malware has hijacked my computer (because also the recovery-cd and defender doesnt work) or that my HD is broken somehow. I would be grateful for any other input you guys might have. Thanks in advance.
Cheers, Oggy