Flashed GTX 970 Video Card works fine on Mac, but not on Windows

I recently bought an EVGA GTX 970 4GB GPU to use on my Bootcamped Mac. I had it flashed through MacVidCards, and now, while it works great on my Mac, I am unable to get any picture to come up when I switch over to my Windows drive. All I get is a black screen and a blinking green light on my display's power button.

Previously, I had been using an un-flashed ASUS GTX 680 which worked fine in both OS X and Windows, I just wasn't able to get a boot screen when I turned the machine on (it went straight to login).

I've already reached out to MacVidCards to see if they have any idea what the problem is and I'm still waiting on a response, but I just thought I'd ask you guys as well.

I've already tried uninstalling and re-installing all NVIDIA drivers from Windows, trying different cable configurations, nothing works. Every time I re-boot into Windows, I just get a black screen. I know Windows is booting because I can hear it's "welcome" chime through the speakers.

Also, I've installed the most recent NVIDIA drivers for the GTX 970 on my Windows, still with no luck.

Help!

System Specs:

MacPro 3,1
2.8 GHz Quad-Core Intel Xeon
16 GB RAM
OS X 10.10.5

Windows 7 64-Bit (Bootcamp, installed on a separate hard drive)

Monitor
HP LP3065

I'm certainly no expert on MacPro video cards, but I do know that certain unflashed PC cards will go straight to log on with no boot sceeen. However, using a flashed card in Windows may entail a different set of circumstances. I would have thought the latest nvidia driver for the GTX 970 should work but since the card has been flashed with a Mac BIOS the driver may not work. It's probably best to talk to support at MacVidCards to see what they have to say. We have a few members who are familiar with Mac Pro video cards and the problems that are encountered when flashing PC cards, hopefully one of them may have an answer for you.