Question PC won't start with GPU it previously worked with

[EvgenS]

Specs:
PSU - 500W (unknown, almost 2 years in service)
Motherboard - asus prime b250m-a
CPU i7 7700k
GPU - MSI GTX1080 Gaming X
RAM - 16 GB HyperX 2133
SSD - 240 GB
HDD - 1 TB
OS - Windows 10 professional
Nothing is overclocked and never touched it


Problem:
I replaced my old GTX1050 with used GTX1080 a month ago and everything worked good until today. I started PC and after windows loaded PC crashed. When I try to start PC motherboard, GPU and fans lights blink for a moment and nothing happens. Fans do not work, no sounds, nothing.
If I uninstall GPU PC starts. Other PC components are fine and windows loads as usual.

I tried to reset BIOS (removed the CMOS battery, shorted the CMOS jumper ) and loaded BIOS default settings but it still won't start when GPU is installed.

I think it could be due to GPU broken and PSU prevents to damage other system components. Or may be PSU is weak for my system (but it have been worked for 1 month somehow) but how can I check to be sure what to buy?

Thanks for your ideas in advance!

 

[EvgenS]

update:
System starts with installed GPU in PCI slot but without connected power cables (6 and 8 pin). GPU light and fans are on.
As soon as I connect power cables to GPU, system does not start (dead)

 

[norcalsc]

i immediately think PSU next would be bad GPU

 

[EvgenS]

The problem was in my GPU power port (or something) but the most probable reason which caused the problem is that I used GPU with weak PSU (500W) for too long and this probably damaged it.

I changed PSU to DeepCool 650W and replaced GPU with used ASUS GTX1070 ti.
My former GPU MSI GTX 1080 gaming X is in repair now and may be it will work again (will see)