systemErr

Likely there's a plastic locking mechanism holding your card in the slot. If you don't care about "clips" or "locks" just give your card a good pull, freeing it and thus breaking anything that's keeping it stuck in the slot. Yes, you may also cause enough force or if your hands slip, for example, you can possibly cause mobo damage. Although I haven't used PCIe, I know AGP slots do require some force on the cards to insert them and take them out.