I bought a second hand monitor off eBay. Plugged in and all fine for a few hours, I then got a vertical hairline top to bottom. rebooted, etc. etc. but problem stayed. Switched off overnight, problem hasn't been back since.
I'd wondered if the main board was failing and this was a sign but Google search doesn't seem to back that up, possibly a cable issue and may never return.
Anyone experience of this? I'd sooner not return it for a refund but don't want to get stuck with it if it fails further down the line!