Beep codes can mean different things depending upon the BIOS maker. Your 3 beeps apparently mean "can't find the RAM". If I'm reading your post correctly you are now trying to boot with only the RAM & CPU installed with no success. If I were you I would first try some known good RAM, only one stick at a time in each slot. If none of that works you have either a bad MB or processor. The only way to diagnose further is to replace one or the other with a known good one.