Booting issue

I am occasionally having a hard time booting up my system, which is approximately a month old. The case fans spin up, it almost sounds like they are revving. The monitor doesn`t click on and the system just idles. I am thinking that worst case scenario it could be due to the power supply or the motherboard. I just pushed in all the connections, so while hopefully it was just a loose connection... does anyone have any ideas?

I hit reset the first time it happened and that cleared it up. The second occurance, I hit reset but it didn`t fix it. I killed the power to the power strip and then it was fine. After the second time I took off the case and jiggled the wires before I tried to power it on just to make sure nothing had loosened up. I have restarted a few times today with no problems. The problem seems to happen after I turn it off for the night. Which I will do tonight, to test it.
I can`t answer the video questions because I didn`t check the GPU at that time, nor did I try to remove the card. I realize that GPU could be defective, but the revving noise of the fans makes me think more PSU. I forget which line carries the "ON" current, I want to say the 5V line (I could be totally off, I have a poor knowledge of electricity). I did check the output earlier and everything looked good, well within tolerance. I want to think it is a loose connector, but that is too convenient for me to count on. Thanks for any ideas!!