No Display on Computer Screen
Solution 1:
Check for any beeping sound inside your CPU, your problem might be a hardware related inside your CPU. In case you hear the sound do a combination of swapping memory slot and trying a new memory or video card in the CPU. See if the CPU boots.
Solution 2:
Check the monitor on other CPU because it might be the problem. Also while doing the checking try replacing all of the cables as well to manage more time. Also if the monitor is on but no display then it is the back light. As long as the light indicator on the monitor is behaving like it should be.
No Display on Computer Screen
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If  you describe in more detail it would be better but still I give you the most happening error: 01. Monitor is not turned on.  02. If your computer at asleep.  03. Hardware problem like damaged AGP card or no driver.  04. Your data connections to monitor from CPU is damaged or broken or not good enough to pass data. 05. Monitor settings are not correct like resolution.  06. Damaged  monitor. You can check it by replacing it and add new monitor. For farther detail’s I give you a link of a site: https://www.computerhope.com/issues/ch000241.htm. if you still do not have the solution go there, where you brought from. I think you have the warranty.