According to the motherboard of that pc, the ram IS compatible with it so if it's not working it's probably dead. Before you send it back for replacement memory though, make sure it's actually seated in place before firing up the desktop. What you want to do here is hold it evenly at each side, and push down on each end simultaneously with a good amount of force until you hear it snap in. Try this on both slots, making sure it's facing the right way. If you still get nothing, request a return/rma or else buy a replacement set. If buying new ram, shop according to what the motherboard supports only.