No Display

I recently formatted my C drive, after which I had a problem with my display card with the error code 10 saying my card was not connected.
I removed and replaced the card and now I have no display, no boot-up, no lights on keyboard….nothing.
What is the problem and solution ??
Fairly old hardware: G-Force 2 mx400, AMD 700 CPU, 256 RAM.
Help, I’m lost without my PC !!!