Will not start, screen blank, power light on, hard drive activity light on for 1sec then off, clicking sound 1sec intervals with 2 beeps. Reset memory, hard drive, optical drive no help
Two beeps mean no memory is detected. Together with the clicking noise means bad mainboard.
Depending on the processor and GPU type, $150-300 for the board; add another $100-150 for labor if you can't or won't replace it yourself.