Hi guys, last night I was busy gaming, my PC froze an when I restarted it, then my PC starts up and everything runs nicely but my monitor don't switch on, the light keeps on flikkering, as if my motherboard crashed or my graphics card

Test the monitor on anouther computer
Start with reseating all the cables. If this dose not clear it start in safe mode by pressing f8 at boot if you can get in in safe mode roll back or reinstall the video driver. If safe mode still shows a blank screen reseat your video card if it is not onboard. If you have a newer high end video card check the power connection if all this fails you need a video card

It does indeed sound like the graphics card. Good troubleshooting would entail plugging another monitor to the computer to rule out the monitor being the issue, then swapping the video for another (that uses the same slot) to test that.

I agree with cmeeks answer. Your video card is very likely at fault.

Does the monitor come on at all even when you first turn the PC on? Do you see the BIOS screen or Windows loading screen?

If you don't see even that much, then besides cmeeks advice, I would also try reseatting your RAM chips. Just be sure that there is no power going to the PC before you start disconnecting/reconnecting anything.

If it all works again but locks up/freezes after a while, then again, think about fitting a new graphics card as this is most likely your problem (though don't rule out the RAM either, especially if its an onboard graphics solution you have).

Hope this helps!