PC won't boot after thermal shutdown

I have a Shuttle SP35P2(V2), with a nVidia 9800GT video card, 8GB DDR2 RAM, and an Intel Core 2 Quad.

I was playing Portal, and my computer randomly powered off in the middle. It was a thermal shutdown. I think the video card overheated. The VGA fan is very close the the cables (SATA cables) and I think the fan is not getting good airflow. This has not happened before so I do not know why it happened now. Anyway, after that happened (and I let the case cool), I opened the case, and removed the video card. I cleaned out all the dust from all the fans. There was a lot of dust in there.
After putting everything back together, I turned the computer back on. It told me the "CMOS checksum was invalid". I pressed delete to enter the setup menu, and the screen went blank with a cursor in the upper left. I powered off the system, turned it back on and it gave me the "CMOS checksum was invalid" error. This time I pressed F1 (to continue), and the same thing happened. Black screen, cursor in upper left.
I then unplugged the power, pressed the power button (to be sure all caps were discharged), then pressed the CMOS clear button on the back. I waited a few minutes, then powered it back on, and it still did the same thing whether I pressed delete or F1.
I do not know what to do, and I hope this is something that can be fixed. I am going to leave the system unplugged overnight, and try again in the morning.
Anyone know what the problem may be and anything I can try to do to fix it?

P.S. "Warning! CPU has been changed. Please re-enter CPU settings in the CMOS setup and remember to save before quit!" Is error message I see.

Never mind. I fixed it. Pulled CMOS battery... waited... put computer back together. It works now.