Sorry, laundry list:
- give details about your system (model, etc) or major components (motherboard, monitor, etc) AND operating system
- download service manual for system/motherboard and for GPU
- if no card before and just running on internal graphics, check manual to see if you have to change settings for an external card to be used
Then, fill us in on history (where system came from, how long you have used, where card came from, was it tested good on another machine, etc) and any developments