@dibl: You are most probably right. Problem is only that I can neither find F-Lock/Function Key on the Keyboard nor within the BIOS to toggle- Other Models have such an key but mine (HP-8470p) doesn't seem to.
The problem stays also when booting a live DVD Image, so it is somewhere hidden in BIOS. Resetting BIOS to Standard also didnot solve that.
The Fn Keys themselfes are acting "normal" but when using the combinations with Alt+Strg+Fnx or Alt+Fnx, the only working combination is Alt+Strg+Fn7 resp. Alt#Fn7. All others lead to freezing the screen until I "return" to Alt+F7.
Searching through some solutions for other HP-Notebooks (on some there was mentioned "Action keys, but that I also didnot have within the BIOS-Setup) did not help yet, but still searching and examinating. :-)
regards
Reiner