There are lot of old graphic cards that are not supported by windows 10 or may be new graphic cards are not supported by previous windows. If your graphic card is not being detected then may be its not dead. Below are the tips to fix the issue.
Check From BIOS
After installing the graphic card, it must appear in your PC BIOS with other hardware. If your graphic card is not appearing then it means it not properly connected or may be not getting power from PSU. Or may be your PSU connector got faulty. First unplug the graphic card and check it on another system. Do not push the connector as it may damage the card if still was in working condition. Clean the card smoothly and rub the end with rubber to remove the carbon. Connect it again and check if it appearing in BIOS. If it appear then check below tips.
Check From Device Manager
Your graphic card should appear in device manager. To open, write device manager in windows search beside start menu and open the program. Check if any unknown hardware or any hardware appearing in other devices. If appearing then install the updated driver. Before installing, you must uninstall the old driver.
Install Microsoft direct x as some time virus may infected the direct x program. Scan your PC with anti virus and install again directX. After open directX by typing dxdiag in windows search and open the program. Go to display tab and check if any VRAM is appearing.
Check From GPU Z
Install GPU Z and check all the display hardware. Check if your hardware is also appearing.