Did you completely removed the old video card driver.
Depending on the brand or model of the board, there are several ways to do this.
1. Install your old card and follow the instructions on this link.
Note that if you do not have the drivers for your card, you should get them from NVIDIA's download section before installing your new card.
Then, install your new card and double-click on the auto-setup for the driver you just downloaded and follow the prompts.