DL2 Display Issue

Good day! I have a DL2 that the display was not working correctly.

Another tech replaced the video card and it was working fine for about an hour.

Then the display was on but would not display anything at all. You could see the glow, but no info.

Now the display is completely blank. Is there a recommended way to test to make sure that the video signal is correct coming from the video card?

Any suggestions on where to check power and signal? Thanks and take care!