no signal to monitor

so the deal is that my desktop doesn't sense a signal to my monitor. i know there is nothing wrong with the monitor because connecting my vga cable to the laptop works fine. When i power on my desktop it takes three tries to actually turn on every time. so: I press power button>on,off,on,off,on. my keyboard seems to get a signal so idk what to do. any suggestions? it's a pretty old comp but runs games just fine. what could be the problem
all help is appreciated

in fact i was going to reset my whole operating system in about a week due to the start-up problem but i cannot do so now since i cannot see what's going on inside the comp(no monitor display through dvid dual cable)