After I changed to a newer video card, shut down and started again my monitor has been dark, no display. RAM, processor, drive are all OK; the video card is in its slot and I have confirmed that all cards are firmly in their slots.
Does anybody have an idea of what I should try next?

I'd put the old card back in and then try using the new card in a spare machine/a friends computers to check it works.

Maybe the card is not compatible with your monitor/computer??

Doing the above should work :)

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