If you're whipping the processor in and out, check that it's firmly seated. Why did you need to clear the BIOS in the first place - is there a history to this that might help us. Otherwise, do as jimv7 says, but cut your system down to the barest necessary to start up by disconnecting any accessories that are not essential. Watch for any onscreen messages however brief they may be (I suspect you're not actually getting that far, but just in case!). Ensure that your motherboard isn't shorting the case (no reason why it should, unless you have a stray earthing or other lead rolling around, or perhaps a lost screw underneath?).