OK, that is some useful information.

If, when you reboot, you can hear audio form the computer, then you know Windows is running. If you cannot see anything on the monitor, then that means that your video adapter driver, or the video adapter itself is not working properly. This might be troublesome to fix, since you cannot see what is on the display.

Does the computer have an add-in video card or is it using the video adapter on the motherboard?

If it is using the video adapter on the motherboard, you could try installing an add-in video card and switching the monitor connection to that to see if you can see the screen display.