anything can be the reason why the computer is not starting properly.
Do you even get any post beeps when you tried turning on your computer?
might sound kind of stupid, but maybe try clearing the CMOS, which is to take out the quarter sized battery out, and leave it out for a good 10 minutes.
worked for a build i did, it would turn on, but no display nor post beeps, then i cleared the CMOS, and it started to work.