The graphics card has failed. Spinning fan means only that the fan works. Says nothing about the rest of the card.
The powersupply has partly failed. ( less likely )
The slot in the motherboard or it's control circuitry has failed.
Test the card in another compatible system.
Test a known good compatible card in your system.
Test with a known good powersupply.
There is one other slim possibility. Your CMOS battery has failed and the BIOS has reset to defaults which would probably not be set to recognize the plug-in graphics. Boot up into bios and check the display adapter settings.
Goin' Fishin' (Some day)