Something weird with the screen

It seems like the screen only works if I turn it on exactly at the same time as I turn on the computer.

So i need to push both the screen power button and the computer power button at the same time.

I am not sure, it just seems to work when I do it.
What can cause this weird problem?

Is it possible or just coincidence?

Have you checked for bent pins on the vga/dvi plug? I'm pretty sure one of them sends a power/sleep signal, that may be the problem. Also, try connecting either another monitor to your pc or your monitor to another pc so you know if the problem is with the pc or monitor.

As Jimbo1531 pointed out on the bent pins, you could also try changing out your cables, whether DVI/VGA.