System no longer booting with gtx 970 plugged in.

If you're handy and lucky, you might be able to find a damaged component on it and replace it. Such as a bulged capacitor. However, many times the actual GPU is just dead, and there's no fixing that. My R9 290 died after 2 1/2 years of use, yet my HD4870 still works after 9ish years.

It is not PROBABLE that it was the cause, but it is POSSIBLE that it MIGHT have CONTRIBUTED to the cause.

Those CX units are not known for being firestarters or having seriously bad ripple/electrical noise, they are simply known to have used less than desirable capacitor selection and occasionally have some poor quality soldering inside. However, ANY power supply, from a Raidmax hunk of crap to a Seasonic Titanium unit CAN have some kind of potentially disastrous failure inside or some manufacturing flaw that makes them either fail or even damage something. Usually though, that is not the case on decent units.

I'd be a LOT more inclined to believe it was simply a failed card. It happens, to all kinds of hardware. Similar to what was mentioned above you could have two identical GPU cards, or motherboards, or whatever, and one might last ten years while the other fails after six months even though both have been used in an identical fashion and an identical environment. Like we always say, it just IS what it IS.

I would think your card should probably still be under warranty unless you bought it used or unless you purchased it very soon after they first came out. Most EVGA graphics cards came with a 3 year warranty, but knowing the EXACT model number would tell us exactly what the warranty was so long as you bought it new and either registered it or have proof of purchase.

Truthfully, I don't see any reputable reviews at all on that Gigabyte power supply which usually either means that it's so poor quality that the manufacturer has refused to send any out to the various review sites for teardown OR it's simply been determined that it's not worth reviewing because it would create bad PR for them. Sometimes it's because the unit is too new for anybody to have gotten around to reviewing yet but honestly Gigabyte does not have a reputation for selling high quality power supplies despite having a very good track record in other areas like motherboards and graphics cards.

The CX, is just mediocre. Plenty of reviews on them, which are not initially terrible at all, they just tend to not live long in anything more demanding than an office or internet browsing machine.

If you are able to get your card replaced OR end up buying a new one, I would definitely recommend a better PSU than either of the ones you currently have. That Gigabyte unit is probably fine for your other FX system as long as you don't have a high end GPU card installed OR to use as a backup for troubleshooting only. Maybe even return it if it was purchased fairly recently.

I would look to getting one of the Seasonic Focus or Prime units, EVGA G2, G3, P2 or T2, Corsair RM, HX or AX, Super Flower Leadex or Leadex II Gold, or another of the tier 1 or 2 units listed here:

http://www.tomshardware.com/forum/id-2547993/psu-tier-list.html

For the PSU or the graphics card?

If you're looking at the warranty info on the graphics card you can just run GPU-Z and find the full model number that way. The last two letters will be the warranty code suffix. I THINK yours is KR but I can't be sure without knowing the model number.

If it's the power supply and you bought it as part of a bundle, then it's probably not returnable, and generally not returnable after 30 days in any case.

Yep, you're right. It's a B stock item meaning it was either already repaired or was refurbished. Looks like you're in the market for a new card but before I made that decision I would probably recommend trying it in another system that is known to be currently working and has a capable enough PSU. If you have a friend that will allow you to try it in their system that might be the best option. Since it didn't work in your other system, so long as that system DOES work with other cards installed, then I'd say it's pretty darn likely you can assume the card is done for.

Getting a new card is likely a foregone conclusion at this point.

Good luck.