I took off the CPU heat sink to blow out the dust. Now I can't get it back on. I've tried everything I red from Google: I pull up the black pins so they're inside the white part before putting the heatsink in place, and then push firmly down. Usually 2 of the 4 pins don't make a clicking noise. Is it possible the pins are broken? I need this computer for work so would buying a new heat sink solve the problem? Here are some pictures. Normally I apply the thermal paste to the CPU but when I moved the heat sink around it got messy and I cleaned it all off, but I'll reapply it before replacing the heat sink.
I know the heat sink isn't sitting on properly because when I turn on the computer I get a CPU over heat error (and have to turn off). Is there anything else I can try or should know before buying a new heat sink? The fan works fine so it's only a problem with the connectors.