If it hasn't been done in the last 5 years, try replacing the size 2032 CMOS battery.  Not sure if it's the card or not, but that's a good place to start.  A low battery will cause all sorts of seemingly unrelated bizarre problems, including boot problems.
I have a Dell Optiplex 9020 MT which I've added a GTX 1050 Ti video card for gaming. It was working fine for months until a couple of weeks ago. The graphics card is randomly giving no signal when booting. I can get a signal from the onboard graphics, but can't game on that. The GPU sometimes works, but I'd have to reboot the computer several times for it to happen. Secure Boot, and Block Sleep (S3 State) are disabled in BIOS, and Boot List Option is set to Legacy, and Legacy Option ROMs is enabled. Sometimes graphics card is not showing up under Primary Display list in BIOS (it only shows onboard graphics). It used to work fine with these settings until recently. When I change boot mode to UEFI, it can't find the boot drive (it says no boot devices found). Any advice on how to get the graphics card to work again would be appreciated.
Dell Optiplex 9020 randomly gives no signal from graphics card!