Monitor Does Not Engage On Boot Up

ive recently started having this problem been googleing it for a couple of days on and off and havent seen a solution for me. I turn on my pc to boot it and power comes on fine. i turn on my my monitor either before the pc or after (either is the same result) but the monitor stays black while the pc goes through the normal booting up process. I know its booted because if i switch on and off the monitor roughly ten times it the picture finally appears.at this stage the pc and monitor work normally.Until the screensaver comes on if i leave the keyboard or mouse for whatever time is set.

then the pc goes black (was mistaken before not sleep mode) if i havent come back to the pc.then the problem is most of the time the picture wont come back.the pc is still on but i have no picture again.then i have to turn the on switch on and off a couple of times again till i get a picture. If i use the pc for a long time period i have no problems as long as i dont let it go to black(think its poewer saving).example put the screensaver to 20mins. Also if i have to restart the pc , doing updates etc the pc reboots fine and the monitor works fine. so basically on boot no picture. on reboot have full working monitor.