On some occasions my PC will not start/boot up. The machine will turn on and "spin up" but will not start the O/S. It will simply run and the monitor does not turn on. After turning the PC on and off several times it will eventually start. Sometime one or two times, other times as many as 15 of turning it on and off. Looking for advise/remedy Thank you.

I would check inside the case for any loose connections, such as power cables to the hard drive. It also could be your psu-what are the specs on the psu ?

If the video isn't displayed, how did you confirm it was the computer and not the video card or monitor? Have you tried another monitor on this machine, or connected the monitor to another computer to test it? Constantly powering off and powering on without properly shutting down will cause your Windows install to eventually become corrupt. EEOC

It's almost certainly a poor connection in either the power supply or on the motherboard. All materials shrink when cooled and expand when warmed. This tends to open up poor connections when a machine is powered off for a while..

Sorry for the delay, work comes first, no choice. First off, I have tried additional monitor and same problem once in a while. When the PC does boot up it is fine and can be restarted several times before the problem returns. I have checked connections and all seem to be okay. I have removed and reinserted the RAM. As far as the psu what info is needed? Thanks all.