"Guppie" needs help - cheapo GPU rig floats upside down too often :)

My simple build "Guppie" is a an A4-5300 cooled by a DH-14 andtwo Sapphire R9 280X's -see my sig. I am running Win7 Home and an open air "case".

I have been running Prime95/Heaven runs as burn-in with no crashes, but when I set the GPUs (no overclock) to fold (no CPU slot) i get everything running fine. Then, after less than 24hrs, I come home to a running, but non-responsive, no picture on-screen rig. I reset, everything runs fine, and after 20+ hrs, I'm back there again.

As for temps, I have been monitoring, adding an extra fan to keep the APU little more below 70C than standard. GPUs looked fine in GPU-Z, although Hardware Monitor see only one, but I noticed on several occations one of the cards throttling to 300Mhz for no apparent reason. Today I had a crash picture on the TV (my test monitor) which showed scary temps on the CPU, but as the PC is not restarting, is CPU temp really the issue?

Any thoughts on other solutions?

Well, I'll be damned! A kollegue told med to cool the northbridge, and I moved the extra fan to blow in below the front of the GPUs, and by now I've had 48 hours without crash or GPU throtthlig (or so it seems). Will continue the watch!