Got a new (at least to me) GPU, and my monitors aren't getting signal from it.

[Lt Mashumaro]

Let me explain in further detail: My brother gave me his old watercooled ASUS R9 390 DC2 GPU to replace my superclocked EVGA GTX 760 that I've had for 5 years. The R9, to be specific, has a NZXT Kraken x31 cooler on it. He also gave me his 850W modular power supply in case mine wasn't strong enough. The only problem is, is that he forgot to give me the rest of the module wires for the power supply so I couldn't use it. It was missing the 4pin connector that goes next to the CPU, so I decided to continue to try to use my CX600.
Here's the problem: After I got everything connected inside, I plugged in my peripherals on the outside and flipped the switch. The GPU has white LEDs next to where the PCI-E power connectors are plugged into, and they were lit up. I don't know if they're indicator lights or what, but anyway. My monitors are both plugged into the card and neither of them are getting signal. Everything else powers up just fine. My main concern is that my power supply isn't strong enough to power everything. I can't tell if it's able to POST, because for some dumb reason, my motherboard didn't come with a speaker and it also doesn't have integrated graphics so I can't look at that either. What's your opinions on this?

PS: I also added two more 4gb ram sticks that run at 1.50v, just for further information.

 

[andreww416]

First words of advice: make sure your monitors are set to the right input
Second words of advice: make sure your BIOS is set for the right input
One other thing: make sure you download the drivers from AMD's website
That should be all if that's not the problem let me know and I can see if I can think of any other reason that the monitor wouldn't be receiving the output.

 

[Lt Mashumaro]

I apparently can't directly reply from mobile, so I guess I'll reply in this way. I haven't changed anything about the input. Everything should still be set to default. I also can't even get to the UEFI to even adjust anything because nothing displays on my monitors. At all. I can't download and install any drivers if I can't even log into my computer, can I? If there is a way to do this, please let me know.

 

[Lt Mashumaro]

I eventually figured it out all on my own, no thanks to you guys! (Just kidding, I appreciate all of the support I've received on this forum, regardless if it solved my problem or not.)
What the problem ended up being was that the RAM that I put in alongside mine had the same voltage and speed, but different timing. It was at 8-8-8-24, while the RAM I had been using was at 9-9-9-24. It was in no way related to my GPU or PSU after all. What I did to fix it was remove the "new" RAM and boot up into the BIOS and change the timings on the channel it was in, and viola! Problem solved.