PC only runs without dedicated gpu!

[Simonliii]

So my PC started crashing two days ago, but that was only under heavy load. Now it won't even boot, however when I remove my GPU it runs fine. PSU is definitely the main suspect but I don't wan to spend a bunch of money on a new one if it's something else that causing it. So I was wondering if my PCIe slot on the motherboard could be faulty or something like that, I really have no clue about troubleshooting when it comes to motherboards. RAM is not at fault, already tested both sticks, first one by one and then both at the same time with Memtest86 and it found 0 errors.
Full Specs:
CPU: i5 3450 3.1GHz Stock cooler
GPU: GTX660
Motherboard: MSI Z77A-G43
Storage: 1TB Barracuda HDD, 120GB SanDisk SSD
PSU: Corsair CX430 v3
RAM: 2x4GB Corsair xms 3
1 Intake Fan
1 Exhaust Fan

Also another thing that I find strange I just yesterday I was able to run Prime95+3dmark firestrike without crashes followed by a gaming session on Far Cry 4 and then The Witcher 3, while it crashes on boot today  

[HoiDaniel]

Your PSU might be a little bit old and not sufficient enough to provide you with enough power.

The only way to find out is buying a new one. It wouldn't hurt you even if it still happens. In the future, that bigger capacity PSU will come in handy.

[yoghurt13]

After calculating a little, your wattage would be 350W-400W-s under load, and your PSU  got a little older or weaker and "lost some power", SO It can't run the thing efficently enough. (Also at boot everything will be at its load,and there is not enough power that's why It won't boot now). Soo, you should buy a new PSU. The EVGA 500B will be a good choice, cheap but good PSU.

[Simonliii]

After calculating a little, your wattage would be 350W-400W-s under load, and your PSU  got a little older or weaker and "lost some power", SO It can't run the thing efficently enough. (Also at boot everything will be at its load,and there is not enough power that's why It won't boot now). Soo, you should buy a new PSU. The EVGA 500B will be a good choice, cheap but good PSU.

 

Your PSU might be a little bit old and not sufficient enough to provide you with enough power.

The only way to find out is buying a new one. It wouldn't hurt you even if it still happens. In the future, that bigger capacity PSU will come in handy.

I'm currently looking at a Fractal Design Integra 650 M. It was at the top of my budget for a PSU but I'm also getting an ASUS Strix 970 really soon so I figured the 650w would give some nice room for OCing and upgrading CPU in the future, plus I hope I'll be able to improve my cable management with it.

[HoiDaniel]

I'm currently looking at a Fractal Design Integra 650 M. It was at the top of my budget for a PSU but I'm also getting an ASUS Strix 970 really soon so I figured the 650w would give some nice room for OCing and upgrading CPU in the future, plus I hope I'll be able to improve my cable management with it.

With a 970 OC you definitely want 500 watts. More than that isn't needed if you don't go SLI bro.

[yoghurt13]

500-600W-s Would be enough for only one GTX970 with overclock, and there would be enough room for a litte CPU overclock too. And the Fractal Design Integra M 650W looks trustworthy, and is a good choice.