1. Do a clean install of your old drivers if you have
2. Update your motherboard's drivers
3. In the BIOS, set graphics to PCI-E
4. Make sure it's installed properly, and compatible with your system (PSU is sufficient, Power cable for GPU is plugged, seated properly, etc)
5. Make sure other components of your PC is fine, do tests first using IGP.
6. Your GPU may be defective, check it on another system. If still it has the same issue, RMA it.