Computer screen distorts and image goes away?

Try to reinstall the video drivers to see if they have become corrupt. There are two different settings in BIOS for video cards, one is to use the one built onboard, the other is to use and external Video card. I am sure you are aware of this. If reinstall the drivers do nat make a differenct, then the video card may be defective. Make sure all the connections are not loose. I had a similar issue awhile back with a Nvidia External Video Card. I guess awhile back Nvidia had an issue with the vendor who made their video cards and some of those had defective chips on them. Don't have any other answer for this question.