Hi all - I've seen a small number of people post up about issues like this, and of those that I found, no one ever posted back with their solution (if they even found one). Basically, I upgraded my 2009 single 2.66 quad core CPU to a w3690, and I am getting a kernel panic on boot (after the chime, but still on the apple logo screen). I am running OSX 10.7, and had no issues upgrading from 4,1 to 5,1 with the firmware utility. Potentially useful info: [li]Kernel panic: http://pastebin.com/2REtkxnD[/li] [li]Hardware Overview from System Profile (after re-installing old processor): http://pastebin.com/z8P8dWZL[/li] [li]kextstat output after OS update from 10.7 to 10.7.5: http://pastebin.com/itVq9ZLp[/li] Stuff I HAVE tried: - Different sets of RAM (I have one set of 1066 3x1GB and another of 1333 3x16GB, both verified working with the original processor). Same KP issue. - Re-installing the w3690 (I thought maybe it was overheating, despite my extremely meticulous cleaning & AS5 application). Same KP issue. - Cmd + Option + P + R. Same issue. - Cmd + Option + N + V. Same issue. - Booting without keyboard and mouse connected (only peripheral is the monitor). Same issue. - Booting from Snow Leopard Install DVD (only one that I have). No luck. DVD spins for a while, and after waiting a while *everything basically ends up halting. No KP in this case. Just sits on Apple logo screen. - Boot in Single User Mode. Was able to get to a prompt one time before system halted. As soon as I tried mounting the the disk, I got a kernel panic. I don't have a log of it, but it was slightly different than the one I normally get; it references a different Kext. IIRC, it was one of the IO*Family kexts. - Switching in the old processor to make sure everything else is still working. Everything works. Using it to write this post. Stuff I have NOT tried: - Removing the NVidia GT120 entirely; it's the only PCIe card in the machine. Nothing else is connected, except a usb keyboard and mouse. - I just realized it now, but this machine was running base 10.7 install (fresh install I guess), and has not been updated. I went through all of the system updates just now, and am up to 10.7.5. Not sure if any of the OS updates could help my issue with the new processor in it. The updates were mostly Java related, and one combined OSX update; nothing firmware related. EDIT: Tried installing the w3690 after the update, and now I simply get stuck at the white apple logo boot screen rather than getting a kernel panic. - Fresh install snow leopard retail (again, only cd i have), and try again. Any further suggestions? Is this CPU bad? Is there anything I can definitely rule out? Is it at all possible that this is still software or firmware based? Thanks in advance!