4x7950 gigabyte stock clocks(1000/1250)
gigabyte 970a ds3 mb
2x4gb ram
sempron 145
lepa g1000 1000w psu
i have two 1->1  risers and 2 1->16 standard risers
12.8 drivers
2.8 sdk
cgminer 3.1.0

Everyhing worked fine when there were 3 gpu(2x 1->1powered raiser and one in 16x slot), after adding 4th one(2x 1->1 powered,1->16 in 1x slot, 1-> in 16x slot) rig just turns off after about 15 minutes(sometimes more sometimes less), temps are ok i use autofan with target temp 75 and they all run at about 73 all the time while mining bitcoin. I can't turn it on for a while.I used it for a while with lcd plugged in and don't remember it happening(maybe it was to short time). Psu is 4 rail and i tried to split is as equal as i can:
1:mobo+one card(not modular so has to be i guess)
2:one card, impossible to plug anythin else
3:one card+ssd+powered riser
4:one card+powered riser

only way to determine the rails was a photo of pcb in some review so not sure it really is split that way.
Looks like something with psu for me but how can it be to small for this setup?