If your open your computer but it shows no power or no display, there's definitely something wrong going on. This problem can be solved easily depending on what has caused it. There are some reasons why a PC monitor suddenly refuses to turn on.

First check your VGA cables which are connected securely to your PC monitor. If there are loose screws, the cables may not held in place correctly, which leads to monitor problems. Tightening up the screws may help in sloving the problem. Otherside, check the UPS has short circuit.

Sometimes, the moitor has own problem . Then you can bring another monitor for testing. If it does work, the problem may be related to the video card. Monitor failure can be caused by a loose video card. First turn off your computer and then try pulling out the video card and inserting it back securly. Check if this solves your problem. Then you can turn on of your computer. If the video card doesn't work properly anymore, you may have to replace it.