Some machines won't boot with the newer GPUs. The 950 and the 1660 have about the same power use on power up so check with your PC's maker about a current BIOS and how to install.
1st the specs.
OS Version: Microsoft Windows 10 Home, 64 bit
Processor: Intel(R) Core(TM) i5-2320 CPU @ 3.00GHz, Intel64 Family 6 Model 42 Stepping 7
Processor Count: 4
RAM: 8174 Mb
Graphics Card: NVIDIA GeForce GTX 950, -2048 Mb
Hard Drives: C: 450 GB (156 GB Free);
Motherboard: Dell Inc., 0GDG8Y
Antivirus: Avast Antivirus, Enabled and Updated
EVGA 500W psu
trying to upgrade to a nvidia gtx 1660 ti gpu. when installed load screen appears but won't boot up. sits there and beeps. updated bios and got same results. plug the 950 back in and it runs fine. any suggestions?