Question Got a new GPU, but it won't always give signal to the monitor

[FunkBlack]

I got an used XFX RX 470 8Gb, I had some problems after install (only had signal from intagrated graphics).
I managed to make it work (not sure how, just some cleaning and windows repair) and after I installed the drivers and had to restart my pc, it won't give any signal, not even from the integrated.
Now every time I restart my pc I have to disconnect the power from the GPU and plug it back (while system is off). It starts no problem.
Later I found out that the reason why I don't have signal from the GPU, is because the mobo switches to integrated.
Where is the issue? The old R7 260X works without a problem.

Configuration:
i5 3470
GA-B75-D3V MoBo
2x4 GB CRUCIAL BALLISTIX SPORT
Zalman ZM700-LM Power Supply

What I've tried:
-Disabling the integrated VGA adapter from Device Manager;
-Disabling Integrated Graphics from BIOS;
-Windows Repair;
-CMOS Reset;
-Windows Reinstall. At this point it seemed like it worked, I restarted it a couple of times and booted no problem, but the next day the problem reappeared.

I've found that this guy (Youtube link below) has the same problem as me, and he fixes it by disabling the Intel HD Graphics, but as I mentioned in the things I did, in my Display Adapters, it only shows something like " Intel VGA adapter" (i can't fully remember, but it had the VGA word in it)

View: https://youtu.be/3rfe0jYSpUg?t=88



Sorry for my vocabulary, Thank you.

 

[rgd1101]

make and model of the psu?

 

[FunkBlack]

It's right there; Zalman ZM-700-LM Power Supply

Update: Won't work by unplugging the power anymore. I have to unplug it from the slot.