LED Lights on Logic Board- 1 & 2 not on?

I replaced a bad logic board and only 3 & 4 LED lights are on...1 & 2 are off. Also when I try to start I get 3 beeps. I have replaced the RAM with known working ram and tried only one stick at a time in different slots..same results! I also replaced the power supply...same results.

Any ideas on what to check next?