Welcome to the forum, guys!
Sometimes, vid card heatsinks are really really hard to get off. The freezer trick usually helps, but it only weakens the glue a little bit. Most of it is just brute force.
Vid cards are actually a lot stronger than you probably think- as long as you don't squash any surface components, you can safely stick a plastic kinfe or credit card or whatever between the GPU core and HS, and t w i s t slowly until the HS pops off.
The trick is to not let the card bend at all when you do it, and no to use a metal tool. A screwdriver, etc. is stronger than the GPU core by far, and will ruin it.
IF you feel you need to weaken teh glue before you can pull off the HS safely, get some canned air and spray it at theglue held upside down- it'll freeze to far below zero in a few seconds
