Hi guys, thank you very much for your quick reply!!
I have tried to run the LiveCD without any boot commands at the very beginning. I see the boot progres bar, but when it's at 100% it just freezes and doesn't accept any input anymore. I started to try with the "noapic" stuff only after I found a post saying that this could help. Unfortunately it didn't
I have checked the md5sum after downloading. I created the LiveUSB using "Linux Live USB Creator" in WinXP. It creates various files on the flash drive, but there is no ISO anymore to check for the md5sum.
Now I tried with all devices disconnected and the USB plugged in the rear slot, unfortunately again without success.
@Just17, I don't understand exactly your point 3 (editing GRUB). How can I do that? (sorry, I'm quite new to all that