malware disabled scanners?

Hey there!

I'm afraid something has infected my computer...

It started to behave weird as any software capable of scanning for malware/ viruses etc. was not working anymore.
E.g. the "launcher" of a famous MMORPG which includes a malware detection routine/ warden. (The game itself is running smoothly, but that launcher is not even showing up when started.)

I then tried to scan for malicious software using
- ad-aware >> no results (except for some cookies...)
- spybot s&d >> resulting in a trojan/keylogger trojan-psw.win32.kates which was removed successfully

Unfortunately I was not able to run a Avira Antivir scan (or any other antivirus) (because it's license (though it is freeware...) was not valid...)
I uninstalled it and tried to reinstall the latest version - no chance. The setup just does not work. No error message. No freeze. But no setup window either...

And there's more - whenever I try to run or install anything that behaves like a scanner (tried Hijackthis, GMER, Malwarebyte's Anti-Malware, Avira Antivir, Combofix/ Kittyfix, DSS, Avast...) there's one common thing happening: NOTHING. Program windows of the scanning software just disappear without any message or the software cannot even be installed at all.

Thus - what now?

I already changed passwords for anything imaginable (mail acounts, online shopping etc.) from a clean computer.
My main concern now is to get rid of whatever is causing the computer to act like this.
There's GB of data on the hard drives (photographer...), no to mention dozens of photo editing programs with individual settings...
If there's a way to get the computer clean without having to reformat it, I'd really appreciate this...
However, if nothing is working I know how to backup and later restore all the data - it's just insanely time consuming...

Best regards and thank you for any help/ suggestion,

SMark

 

Sry for being impatient... I am currently going through the READ & RUN ME FIRST, will post the logs and results later.

SMark

 

Unfortunately I cannot edit my previous post, sorry for bumping my thread, this is not intended.

Well, after running all the steps from the READ FIRST sticky ... all is going well again now. I do not know what the scans have found and removed.
ComboFix deleted a couple of files, and after completing the last steps from the sticky I was able to install an antivirus software which found a couple of trojans on the computer, all were able to be removed.
I was as well able to run Anti-Malware, which didn't run previously, with no findings. SUPERAntiSpyware didn't find anything either, and it seems that everything is now functional.
The launcher mentioned in my first post is working again as well....

Thank you for the excellent step-by-step instructions, that helped me solving this issue and sorry for opening that thread even though - in the end - it was not even necessary.

SMark