OK, here's a little fun I learned from a good friend about SGIs, electronics, and the importance of using the right tool for the right job, even if the tool doesn't look right at first! The goal is to get that processor out of the socket, and back in again with out breaking anything, or spending 300 dollars on a state-of-the-art Pin Grid Array extraction tool. 
Step 1, remove the heat sink by prying the four spring clips and lifting it off. 
Step 2, check for heat conducting paste on the top of the chip package. Often it's dried out, you _really_ really_ should get some to replace it. Alternatively, a conductive pad may be present, these can tear when seperated from the heat sink. 
Step 3, THE TOOL. Get a big one! The bigger the better. 
Step 4, heres the trick, the socket has two parts, a white piece which together with the ZIF pin contacts is secured to the PCB, and the black part which slides right to left (in this picture) about an 1/8 of an inch. The idea is to get the left end of the pliers in contact with the white part, and the right side in contact with the black part....... then SQUEEZE... and POP! 
Step 5. Check the pins and the socket for damage. The chip be free of restriction, and remove easily. Hwever it maybe stuck, gingerly wiggle it... it should lift _straight_  out. 
Step 6, reversing the process, replace the processor (again it should drop right in, make sure the socket is in the open position, it is not spring loaded) postion the left end of the pliers on the black part of the socket, and the right end on the white part... and SQUEEZE.... POP! you're done!