sounds to me the 980 is not getting the power it needs but from my experience BSOD errors normally point to system ram problems if you can try out a bigger power supply first just in case the 980 needs more power then its getting from your power supply.
 
then again you are running older hardware I would also make sure I was running with updated drivers and bio's for your MB just to be on the safe side since older hardware is known to have problems with new hardware.

You should start a service ticket, it sounds like some component on the 980 has gone bad and has become temp sensitve. If you get EVGA to RMA the unit, you can have a new one in a few days if you can afford a $500 hold on your CC until they receive the return by using cross ship. This is also a good way to go because you can use the box they send the new board in to return the defective one. I recently had one of the GPUs on one of my GTX 690s fail and EVGA replaced them both with 980 gtx acx 2.0 boards (3842-2983) because only replacing one would break my SLI setup. The only other thing you might try is to find a friend with a newer system to let you test the 980 in their setup. You should also see if it fails while running one of the EVGA OC SCANNER benchmark programs (in RUN mode). Run it with the artifact scanner on. 
 
FYI: two GTX 980s in SLI mode score ~21,000 on the 3D Mark Fire Strike benchmark. The TitanZ, Titan X, and GTX 980 Ti all come in around 15,000. The scores of everything from the GTX 550 Ti to the GTX TITAN X are shown .

What is the bsod stop code you're receiving?

So running your older 680 gets rid of all the issues the 980 causes? Have you monitored your +12v inside the bios with the 980 installed to see if it fluctuates more than .05?

n111ck

Sajin
So running your older 680 gets rid of all the issues the 980 causes? Have you monitored your +12v inside the bios with the 980 connected to see if it fluctuates more than .05?

Yep, no problems with the 680. How do I monitor it?

#1 Have the 980 installed & connected properly.
#2 Load the motherboard bios.
#3 Goto pc health status and monitor the +12v for a few minutes. 

No overclocks on cpu or system ram?

Ram was running at 1002 before the problem occurred? 

Have you tried running the card at reference speeds?

Might want to try testing the card in another system to see if the problem follows the card to another system, or you could just rma it since replacing the card with your 680 resolves all the issues.

Just seen that the 680 actually uses more power than the 980 so I am discounting the PSU and given the RAM / CPU are fine with the old card I think the blame lies with either the card or the driver. However no more crashes since yesterday (fingers crossed) so will monitor and RMA if it starts again.
 
Power Consumption:
GeForce GTX 980165 Watts
Geforce GTX 680195 Watts
 

Yep - board is old and the bios hasn't been updated in ages.

Just crashed again :( - resetting RAM speed to see if that helps.

Good news - resetting the RAM seems to have resolved the issue - have played Witcher 3 for well over an hour with no issues. For some reason the game is now using a lot less RAM - presumably stressing the RAM was causing the crashes. Will monitor for a few days but looking good so far.
 
Have to say the card is excellent - particularly the cooling 

n111ck
Good news - resetting the RAM seems to have resolved the issue - have played Witcher 3 for well over an hour with no issues. For some reason the game is now using a lot less RAM - presumably stressing the RAM was causing the crashes. Will monitor for a few days but looking good so far.
 
Have to say the card is excellent - particularly the cooling 

I'm shocked that you actually got this working on that old motherboard. Most motherboards with that chipset have a hard time working with any video card above a GTX 750i. Kudos to you for making this work!