This will be a longer trip....
I got the new card, and yes, card was around 1 cm too long, even though the Asus homepage said, the 970 was as long as my current 570. '!§%$*+!!!!!
So I stripped the cover of the 970 to see if the errors are gone. Plugged it in, no more picture on the monitor, it stays black.
So I plugged the old card into the second PCIe slot, works. However the second PCIe shares resources with other things (IIRC USB) and I have a constant noise whenever I move the mouse. So it seems the first PCIe socket was causing the problems.
Okay, searched the web for new socket 1155 boards, not many left, only used ones, which I don`t want. Finally found a dealer who had some Asrock P67 Pro boards left, came today, really brand-new. Drove to a local small computer shop and bought a used PC case for 15 €.
I will build the new one over the weekend, as Monday is a holiday here.
My plan is un-installing the chip-set drivers on the old board, plugging the new system together and trying to get away without re-installing Windows and all the stuff. Hope it works, but as both boards have the Intel P67 chip-set, I`m quite optimistic.
Wish me luck, it`s the first time I`m pluggin a PC together by myself.