PC Monitor Fades to Black?

after starting my pc, the monitor fades to black after a few seconds. i haven't tested if it's the monitor or the video card that is causing the problem, so i would like some instructions as to find out what is really causing the problem.

my graphics card is NVIDIA. and my monitor is more or less 4 years old. prior to the day this problem occurred, i removed my graphics card and all for a clean up, and in the best of my abilities, placed them back. a few hours later, my monitor started blinking for some unknown reasons (not really blinking, more like it dims a bit, then goes back to normal). thinking it was just a power surge of some sort, i dismissed it. then in the middle of my game after a day, the screen fades to black. nothing else seems to malfunction, just the monitor. the game did not crash. the light indicating my monitor is on (blue) is still showing. i restarted my monitor, but when i turned it on, it is a little dimmer and after a few seconds, it fades to black again. it could be my placing the graphics card back on, but i re-did that a few times and no changes (i have removed and replaced the graphics card before, that was not my first time). i restarted my pc, and the monitor works until a few seconds then fades to black again. when i turn my pc off, it shows the message No Signal just like it does when i turn it off back when it is still working fine, indicating that the black screen only occur when my pc actually process at start up and so on. i tried re-plugging the wires of both the monitor and graphics card to no avail and is currently out of my wits as to what to do.

replacing the monitor will be my last option, so if any other tests or solutions anyone could offer me, i will be grateful.