Step at a time. Put it back to stock. Test it.
Replace just the RAM. Test it. (Funny feeling that's the issue.)
Put RAM back. Replace the HDD. Test it.
Put HDD back. Replace the SuperDrive. Test it.
If it doesn't freak out, then replace two at a time. RAM + HDD, then RAM + SuperDrive, then HDD + SuperDrive.
You know all three freaks it out, so no need to test that.
Isolate the fault.