Q: vertical line on screen

Hi,

Might be a good time to run the Apple Hardware Test

I'm not too surprised that it didn't register in the hardware test. It sounds like a row of dead pixels, which unfortunately is a sign of a faulty display.

To verify it's not a software issue, boot into Safe Mode by holding Shift while you power on the machine. It will boot very slowly, but don't worry, that's what it is supposed to do. If it is still there, the odds of you have a faulty display are very high.

If that is the case, schedule an appointment at either the Genius Bar or an Apple Authorized Service Provider: https://locate.apple.com

Good luck!

What specific model Mac?

What graphics card is installed?

What monitor and how is it connected.

Does the line appear in a screenshot?

Note this is the Mac Pro desktop forum.