Mining rig freeze after 2 minutes

Hey

I have the following hardware in my mining rig:
- Intel Core I3 4130
- 4gb Crusial Ballistix
- Corsair CX 750W 80plus bronze
- 2 * XFX Radeon HD 7970 DD Edition
- Windows 7 64bit

I have the 2 graphic cards in my pc. They are both undervolted to 0.975V. GPU engine at 854 and Memclock at 799. I've also tried the default speeds of the card (GPU 925, MEM 1375 and 1.175V). Drivers are 13.12 and I've tried 14.2.

I was running with those settings stable for 6 weeks for a couple of days at a time.
Since a couple of days cgminer (I've also tried BFGMiner) freezes after about 2 minutes.

I've tried running the cards separetly. The issue is on the first one. When I run cgminer only on the second card the pc is stable for more then 12h (before I stopped) around 75°, when I run it on the first card (primary) it freezes every time and temp shown is around 70°. I have the same issue when I try to play games.

I don't think that it is the PSU since I can run perfectly on the second card.

Could it be that it is because I don't use fake dvi plugs? Although windows recognizes and activates both 3D cards and the system was fine for 6 weeks.

Any help would be greatly appreciated.

Thanks

Setting that ran fine for 6 weeks before:

{
"device" : " 0",
"gpu-engine" : " 854",
"gpu-memclock": " 799",
"gpu-vddc" : "0.975",
"gpu-powertune":" 20",

"log" : "2",
"scrypt" : true,
"gpu-threads" : "2",
"thread-concurrency" : "8192",
"intensity" : " 13",

"auto-fan" : true,
"temp-target" : "70",
"gpu-fan" : "0-85",
"temp-overheat" : "85",
"temp-cutoff" : "95",

"api-allow" : "W:127.0.0.1",
"api-listen" : true,
"api-network" : true,
"api-port" : "4028",

"pools" : [
{
"url" : "xxx",
"user" : "xxx",
}
]
}