Take it down to one stick of RAM, and put that in the farthest slot from the CPU socket. Do whatever you're doing to test that's getting you these errors. Note your results and move on until all DIMMs are tested in all slots. Once you've gone through each DIMM individually, start running all of them at the same time. Make sure your RAM is configured in a way shown in the motherboard manual (i.e., not side by side on a four-slot board).
If one DIMM makes it through all of the slots fine but the other doesn't (assuming you have two DIMMs), you have a bad DIMM. If both DIMMs are failing on the same slot, you have a bad slot, and that usually means that you have a bad motherboard). If both DIMMs make it through without crashing, something else is up, probably your board itself. If both DIMMs crash on everything, motherboard issues.