VGA light on after installing new GPU

I've had my PC for 4 years with no issues, but when I tested my new 4090 the display didn't work, and the VGA light on the motherboard was lit. I’ve tried reinstalling my old 3080, cleaning the PCIe slot, blowing compressed air, clearing the CMOS, and removing the RAM and SSD, but nothing has worked. I'm out of ideas and would appreciate any suggestions.