Why did the computer stop responding to the connected monitor?

Question

Video cards

Suddenly the monitor or system unit stopped responding to the connection. It says "check cable signal". I checked, everything is fine. Changed the cable, nothing happened. I re-plugged the cable into the vidyuhi, which is on the motherboard, the same thing. I connected the monitor to the laptop, everything works. The reason is in the video? How else to check if there is no additional monitor or system unit.
Win 10, nVidia 9800GT graphics card.

Answer 1

After turning off the computer from the network, pull out the BIOS battery, pull out the video card, connect the cable to the built-in, then press the power button several times with a pause of 3-5 seconds (when the computer is turned off from the network and without a battery!). After that, return the power to the computer and try to turn it on. If it does not help, write, let's move on to the second method.