Thanks for the suggestions all....I've done the following:
- Checked card is seated ok. Pass.
- tried another game. DDO crashed within 30 secs or so.
- Checked power connectors (2x 6 pin) are both all the way in. Pass.
- Card is a Zotac brand.
What I have tried:
- Validating game files
- Running in a lower resolution
- Leaving the computer off for longer after the last crash (damn those capacitors)
- Leaving the side panel off.
- Using a 2x Molex to 6 pin power connector for one of the 6 pin power connectors. I don't know if it matters but both 6 pin ran off the same cable - they looked to be daisy chained?
Game is running now - at least I managed to get out of the station.
No clue what happened. I still think its going to crash any second though.
Nice, seems you tried a bunch of things. Though the GTX970 is a pretty power-efficient card I'd have a better time dismissing power as a cause if you could use non-daisy-chained power cables. Does your power supply have another set of PCI-e cables? If so then you can use one connector of both cables. What brand is the PSU by the way? (apology if you mentioned that earlier.
At least DDO helped in making a case for a non-game related issue. That means we're at the basic hardware stability testing level instead of the game/driver level.
If I were you I'd download HW Monitor from CPUID.com and leave it open while playing the game. Best would be to also enable writing-to-log just in case your PC crashes, that way you don't lose the info.
While playing the game, or trying to play the game, HW Monitor will collect information on your system such as CPU and GPU temperatures, fan speeds, and system voltages.
I doubt that heat would be a major factor here since you'd probably also notice a lot of fan noise if that was the case. The voltage readings can be of use in determining whether or not the PSU is up to the task.
Though a 500w PSU is more than adequate for a GTX970 I have seen generic-brand 700w PSUs die when facing a 400w load, and I've seen well-known-brand 500w PSUs deliver a solid 600w of power without breaking down.
What you are looking for are the readings for the 3.3v, 5v, and most importantly the 12v lines. Ideally all the read-outs for these lines are 3.3v, 5v, and 12v respectively (big surprise right?).
HW Monitor will tell you the current, min, and max value for every sensor it finds so it's great for diagnosing stuff like this.
Don't be alarmed if the above-mentioned voltage rails are higher or lower than what I've stated, they are allowed to be a bit more or less (i believe 5% on the 3.3v and 10% on the 5v and 12v lines) and the exact 'diagnosis' depends on the big picture.
Of course I hope the game keeps running fine and your PC never gives you issues. If it does give you more issues, see if you can get some voltage read-outs with HW Monitor

.
Note: Software voltage readings can be unreliable. Best is to actually use a tried&true&proven&calibrated voltage meter used by certified (wo)men in white lab coats, but when those aren't available, it's better than nothing!