Crossfired my 8750's but second monitor is not functioning properly

[Dogtag]

So I have just Crossfired my 2 Powercolor 7850's and I have both of my monitors working off the top card in my system but ever once and a while my second screen will start to have lines go parallel across my screen until the monitor keeps loosing signal, black screen, loosing signal, black screen and so on for around 5 or more minutes. I was thinking it could be my PSU seeing its only 650 watt but I'm not to sure. Any help would be great thanks.
System-
I5 3570K OC 4ghz
8GB Corsair Vengeance 2x4GB
Asus P8Z77-V LX
2x Powercolor 7850's
650 watt PSU
500GB hard drive

 

[thekyle64]

Are the cards over clocked? what temperature are the cards at when they start to make artifacts (lines, freezing, ect.)

 

[Dogtag]

Are the cards over clocked? what temperature are the cards at when they start to make artifacts (lines, freezing, ect.)

The cards are not overclocked and run at around 40C constantly unless under stress but they dont go higher than 50C

 

[thekyle64]

do you have another psu that you could try to see if the psu is the problem