Hi,
There can be several reasons causing this issue:
1. Driver not installed correctly.
2. HDMI cable being faulty.
3. card itself having issues.
I would suggest to:
1. Install DDU.
2. Boot in safe mode with networking.
3. Uninstall display driver via DDU.
4. Reboot in safe mode with networking.
5. Installing a working GPU driver from Nvidia in safe mode itself.
6. Try to reboot normal and see if the issue is fixed.
If your issue is still not resolved. Try using a different GPU to see if it is a faulty GPU or try changing the HDMI/DVI cable to see if cable was the problem.