Have you checked all these things? If you have more than one DIMM, try removing one. Have you tried booting from a CD? What kind of power supply do you have? Hard drive?
I bought a gigabyte GA 990 FX motherboard and an AMD4100 four core CPU to replace a gigabyte 880 motherboard with an AMD 1055 6 core CPU (which worked fine,just wanted more speed) but the computer won't boot,it goes until the screen flashes blue briefly then it turns off. This is the second set of components that I have tried with the same results,any suggestions or help?