Computer monitor problems can be very hard to troubleshoot - I mean, if your monitor goes blank, how do you check anything on your screen. So that's why it's important to have 2 monitors in the house. Usually, if I have my desktop PC's monitor going blank, I'll immediately hook up the video card to another monitor. If the screen remains blank, then it could point to a video card problem. If the new monitor displays an image, then it's probably the first monitor that has run into problems.
Reason 1: Wetness
The number one reason why computer monitors go blank is - wetness. Believe it or not, when your computer monitor is exposed to humid air, sometimes water can condense and accumulate in the monitor. This causes the monitor to malfunction and go blank. I've had this happen to my desktop PC at least three times before. What you need to do is to leave the monitor alone for some time and allow the water to evaporate. That usually solves the problem.
Reason 2: Faulty Graphics Card
The next reason why your computer monitor goes black is due to a faulty graphics card. The best way to detect this kind of problem is to connect up a new monitor to your PC, then check if you have a blank screen. If you continue to have a blank screen, then it's likely your video card is faulty.
Reason 3: Faulty RAM
This one is less obvious and less common, but it can happen. You might sometimes get bad RAM modules which prevent your PC from booting up even to the basic BIOS startup screen. To detect this kind of problem is more troublesome, you might need to remove those RAM modules and insert them into another computer.
Reason 4: Loose Connections
Another reason why your monitor goes blank is due to loose connections. The connection from the monitor to the mains is usually a culprit, as is the connection between the monitor and the video card. Check those connections before you declare your computer monitor as faulty.
Reason 5: A Short Circuit In The Motherboard
And the final reason why your computer monitor goes blank? It's possibly because of a short circuit in the motherboard. This is the most undesirable outcome of course, as you might have to replace your entire motherboard. However, it's possible that this can happen - so keep your fingers crossed and hope it doesn't happen to you.