BTW, it's a 650W PSU. I suspended BOINC, shut the rig down, put the MSI card in the lower slot, booted it back up. I verified both cards were in device manager, updated the Windows score (went from 3.9 to 5.9), rebooted, opened BOINC and let it run for a few minutes on the one card, then closed BOINC and edited the XML file to run on both cards. It seem to run fine for a while and I left. I came back a few hours later and it was locked again. I shut it down, took the Sapphire card out of the top slot and left the MSI in the bottom slot. I started it up and let it run. I saw it blue screen a few times with a "reference by pointer" error. EDIT: MSI card is this one: http://www.msi.com/product/vga/R7770-PMD1GD5.html Sapphire card is this one: SAPPHIRE Radeon HD 7770 GHz Edition 1GB 128-bit GD... MSI card has no crossfire connector on the board, but the Sapphire does. Could that be something to this? Also, now I am running the MSI card back in the top slot, and it seems to be stable. I also swapped around the PCIe cable and am using the one that was on the Sapphire card right now.