ways to reuse old Dell heatsink

If you cannot wait to set up a test rig but you do not have a heatsink cooler, but you have old Dell oem heatsink, can you use those?

yes sometimes.

I need to install a LGA775 heatsink on XPS 730, but no compatible heatsink at hand.  I have an old Dell vostro 200 motherboard that has LGA775 heatsink but it has M3 threads for Dell built in M3 backplate.

so here is a way: use a needle plier to twist off the metal guard ring on the screws.  once the rings are gone the screws are free to be removed.  now you have a heatsink without M3 screw and you can insert new screws to work with your new mobo backplate.