I got a bit of a problem with a new Antec, Nine Hundred 650 case I just purchased.
When I try to install a PCI v1 and when it fits tightly in the slot it's pulled away from the case enough that you can't screw it in. I've tried this a couple of PCI v1 cards I have laying around. All do the same thing.
I've removed the motherboard, made sure all the brass raisers are all the same size and no luck. My next step is to install the board in an older case and see I have problems there. It's a bit of a pain because the system is up and running fine.
Could the case be not square? Any other suggestions?
Do you have any other cards your could test with? There is the possibility that the case is not square but if you have another card you can test that slot with to see if its square or test that card in another slot and see if the probables are consistent with all the expansion slots.