It would be helpful to get details on exactly what you have.
In particular, the make/model of the psu installed in the pc.
Go back to basic testing.
1. Remove the 570 and boot using integrated graphics.
If that works, good, at least you still have a working pc.
2. Install the 570, but do not connect the monitor to it.
If your installed psu has 6 and 8 pin cables, connect them.
I surmise that the psu does not but try powering on anyway with your monitor connected to the integrated graphics.
If you see a display, good. If not your 570 may be the problem, or the psu you have declined to describe is likely the culprit.
The make of the power supplies is important.
A poor quality unit will not deliver advertised power and may have caused damage to other parts.
The fact that things seemed to work before is indicative of some damage being caused by the jury rigged setup.