|I am still trying to understand why the processor was removed if there was not apparent reason. If there was not prior problem and you were not planning to replace/upgrade it, you should have left the CPU and heatsink attached to the motherboard and used a compressed air can to blow out any dust. Being that the CPU was removed, there could have been a problem with a bent pin/contact (not sure what AMD is using here) during removal or reinserting. There could have been damage when you powered up the MB without the CPU in place (contact MSI for advice on this). If you did not properly remove the old thermal compound and properly apply new thermal compound, the CPU would only power up for a few moments and possibly shut down due to internal heat quickly building up.|
For further investigation, try booting with the hard drive removed, if everything else is OK, then it will be able to boot to the BIOS set up.
Also try booting up without the memory installed, it will give you a beep tone or warning led flashing on your MB.
You have to be a little bit crazy to keep you from going insane.