You should elaborate a bit more. What EXACTLY happens when you boot ? 'Starts up' is a very vague and doesn't mean much to us. Does it POST ? In case you're not sure, usually the PC makes a single beep when it has succesfully 'POST-ed'. If it gives more then 1 beep, then it's actually telling you, in 'secret' code, that something is wrong. If it doesn't beep at all, then something else, perhaps more serious, or perhaps less serious, is going on. You should list your components, and make sure everything has been hooked up to the PSU as it should be. Try to be as detailed as possible, lots easier to help that way.