I had a keyboard failure on start up

Question

after talking to a couple of techs i decided(they said it was done) to change the motherboard. i ordered it from dell and made the switch.now my power lite is orange and i get nothing.the lights on the board are on and the videocard fan is spinning.when i bought the system it came withRaido 2x160 hard drives.after a hard drive failure the tech (it was under warranty at the time) changed the hard drives from raid to i dont know. i dont know if that matters or if i left steps out help please