I've only just started mining and I've lost 4 graphics cards what am I doing wrong?
I'm using an i3 processor 16gb ram a 850 watt gold psu (I'm only running one card at a time)
Bfgminer tuning at 75 percent and 0 intensity. All cards show video with artifacts 2x 7870s 2gb , 1x 7850 1gb, and a sapphire nitro rx 460. Bfg miner says they are sick or dead I put them in another computer but same results.
I'm kindof  new to this and I want to know what I did wrong.

Did you try using each one separately and check if the same thing happens? Did you try other driver versions? One possible cause of this might be the completely different GPU series mix, it's not ideal to mix 7xxx series with RX and so on.
There is also a small chance that your PSU might be on the limits, does that happen when your PC is on full load?
I've summed up all your GPUs full load wattage consumption which totals 800 Watt, you have a 850 Watt PSU + your CPU and every other component probably sums it up to 850 Watts.
Also, did you OC them? Mine get artifacts if I overclock them above a specific point.