OK, no beep the first thing a machine does when it turns on is acccess the bios for start sequence and initialises the CPU. If the CPU is not seated properly or the heatsink is not attached right the machine will not even give a post beep. Double check that, then make sure all the cards and memory is seated securely. Tell us exactly what the case lights do, any sounds like hard drive access or anything that could give us a clue where the startup fails. Might help to clear the CMOS via the jumper or removing the battery for a few seconds.