Did you turn your computer and found no signal on the monitor !!! That what we call it POST (computer don't send signal to monitor).
Some times this problem can be caused by the monitor or the cables, but
If you have issue like this we can do a simple diagnostics and check the
hardware to know what part is bad and replace it.
1- CPU.
2- Memory.
3- Motherboard.
4- Sometimes monitor or cables.