Monitor has lines and colored squares. Can not see anything on screen. Have to totally unplug computer to clear this out and use computer. Now that won't work

Monitor has lines and colored squares. Can't see screen. I have to unplug computer it will not turn off or restart to be able to use computer. Now that doesn't work

Issue with monitor or video adapter, maybe possibly the cable. Have you tried another monitor?

Issue with monitor or video adapter, maybe possibly the cable. Have you tried another monitor?

I had put monitor and cord on another computer and they work

I had put monitor and cord on another computer and they work
That narrows it down a bit. Perhaps the video adapter has issues. If your computer has a discrete video adapter, meaning one that isn't integrated on the motherboard, physically remove it, check the interface slot for debris, and then reinstall it. If you have another video adapter, it can also be tried in place of the original one.