GPU Dead after some hours working (please help me)

[iqacid]

hey there

i run my new rig today.

power: 1350
mb: 990fxa gd65
4x 7950 asus
6gig ram

all thing work correctly with (HW:0) till i got shoutdown twice last night

my setup was

setx GPU_MAX_ALLOC_PERCENT 100
setx GPU_USE_SYNC_OBJECTS 1
cgminer --scrypt -w 256 --shaders 0 --intensity 19 -v 1 -g 1 -l 1 --lookup-gap 2 --thread-concurrency 22400 --gpu-vddc 1125 --gpu-engine 1150 --gpu-memclock 1700 --temp-cutoff 90 --auto-fan --api-listen

and ive changed it to:

cgminer --scrypt -w 256 --shaders 0 --intensity 19 -v 1 -g 1 -l 1 --lookup-gap 2 --thread-concurrency 22400 --gpu-vddc 1125 --gpu-engine 1100 --gpu-memclock 1500 --temp-cutoff 90 --auto-fan

it woks for while till after some hours my first Gpu dead and i restarted pc and it works again

all temp are under 75 so dont think its becuase the heat. btw i use 3x pci express 1x to 16x and one of em is powered and the gpu who will dead after some working connected with that powered one

could be this prob cus for that powered riser? if not what prob do i have? can my gpu have prob? if yes why it works fine for 5 or 6 hours without any problem?

Edit: sorry for my bad english and thanks for reading

[iqacid]

so it seems no one want to look and help me 
please if you kno what is my prob let me kno

[Wipeout2097]

all temp are under 75 so dont think its becuase the heat.

75ºC is too high.

Take a look at gpu-z "Sensors" while mining. You will see you're using too much power and/or taking the VRM temperature too high. Voltage oscillates, conditions change and the core locks up.

You should undervolt with vbe7 and use a large fan blowing at the cards.

Of course it can be the PCI-e riser. Switch cards and see what dies.

[SheepOnDrugs]

75°C is not too high, what are you talking about?
Mine been running on 80 for months now.

[Wipeout2097]

75°C is not too high, what are you talking about?
Mine been running on 80 for months now.

We are not talking about your card. We are talking about OP's unstable, overclocked card. Please don't crap the thread or assume the task of helping the OP.

[iqacid]

thanks for reply

i just test my rig and kept the temp max at 65 but that gpu dead again after 2 hours.
i found a riser but its powered like that one alrdy used. it runned like 2 hours ago while am monitoring it. hope it works

[SheepOnDrugs]

Try increasing your voltage or decreasing the settings until you find a spot where it won't go dead any more.
Some of my cards go dead too if I have them undervolted too much.