In the mean time I was just using single channel 2x 512 MB RAM, resulting in a stable system.
I ran HitmanPro and Antimalwarebytes together with stinger and my own virusscanner, all resulting in no threads.
I updated XP with the latest updates and installed Office 2003.
I then started with restoring the documents and did a restart. After that, the computer was running (but not used) a whole day without problems.
When I wanted to open a new user account for the first time, I directly got 2 errors for process of Windows that did not work properly (I thinksomething with system32, but do not remembre the exact errors).
From this, I got suspicious and started antiwalmarebytes: While scanning the windows system 32 folder, it kept on finding threads (500 and up) before I again got a BSOD:
Then I booted up in safe mode and do another scan with antimalwarebytes, which now did not give any result.
Also TDSS Killer did not give a thread (only with 'signature verification' on it found 1 unknown thing which probably is nothing.
Stinger gives the message that it did not scan for rootkits when I tried to use it and running together with antimalwarebytes, the system suddenly shut down.
Today, I again tried to run hitmanpro and antimalwarebytes in safe mode with networking. Hitmanpro found 2 tracking cookies and durin scan of antimalwarebytes I again got a BSOD:
Hope maybe now someone can give me some advise / help me?