So, what I found out is that the problem was caused by the installation of Alcohol 120%, since it may not have been the newest release of it which is claimed to be Vista compatible. Anyway, I was astonished by the reaction of Vista. I mean, it cannot be possible that a whole operating system crashes completely down, just because of the installation of an incompatible application. I mean much nicer would be to have some error-message before, wouldn't it?? *confused* And the best was that it was neither possible to start Vista in safe mode, nor in safe mode with the command prompt...I could immagine that many people, switching from Windows XP to Vista will get such nice surprises and they probably will pass some time in front of their broken machines, trying to fix such issues. :)
The only thing which is nice and simple, is the solution to this problem (if it works as it did in my case), however you have to know it :). I basically inserted the Windows Vista installation disk and when starting the notebook I booted from that disk. So the Vista installation starts. Then there should be a point targeting everything which has to do with repairing the current Vista installation or updating its drivers etc... I actually don't remember exactly the name...you basically should arrive at a point where you can set back your system to a previous created "recovery point". Select the recovery point which was before the critical installation or at a point where you know that the system worked seemlessly. Then just follow the indications, remove the installation disk and restart the operating system. Everything should be fine then.
There is also a link to a wiki describing the compatible applications, which may be interesting to check: http://www.iexbeta.com/wiki/index.php/Windows_Vista_Software_Compatibility_List