Motherboard issue, RAM, video card, or CPU?

I recently purchased a desktop with a MSI K7T266 Pro2 motherboard (relatively new). It has a AGP graphics card installed and 1GB of RAM. There was an AMD Athlon processor installed when i got it, but the processor was burned to a crisp (black on the back). After installing another AMD Athlon (a step down from the previous processor), the computer leaves me with a blank screen (monitor stays in standby), fails to POST, and gives no beep codes whatsoever. So far, I have changed processors, changed video cards, replaced RAM, changed PSU, changed hard drives, changed flat ribbon cables, reset the CMOS and replaced the CMOS battery. I still get the same thing. The fans turn, the Hard Drive runs, but I never get anything on the monitor. The monitor stays in standby, even though everything else seems to be running fine. Lastly, the CPU light on the desktop stays on for about 45 seconds and then goes off. I think that the CPU light going off has more to do with the fact that the computer never POSTs or beeps. This particular MSI motherboard also has the 4-light indicator on the back when it has a problem. All 4 lights stay lit with the computer running. After checking MSI's website, it says that the processor is not seated properly, but this is a farce. AMD processors' pins fit directly into the socket and it latches fine and has no sign of looseness. Any ideas?