PC turned on but does not boot/monitor no signal

Hello,

I turn on my PC, all the lights are on (case lights and motherboard lights) but my monitor remains off/unable to find a signal. I fiddle with the parts inside my computer, making sure all of them are secured, plug out my power cables and waited for awhile then plugged them back in and it usually works. On the first boot, it will always crash on the desktop, the second boot will be fine. On some occasions, the pc will restart itself while I was playing video games and I have to do all of the above again to get it to work. I have had to do this every single morning for the past few months and it's driving me crazy. I'm sorry if all these symptoms are to vague.

HELP ME. Thanks