A have a coolermaster V700.
So i'm thinking about the pool, but seems fine.
Is that a 700W PSU? Probably not enough for S5. 12 volt rail won't have full 700W.
According to the specific the 12V rail has 696W
Are you using four separate cables?
Should i buy 2more modular cable?
Yes, you should have four cables. Pushing close to 300 watts in one cable is simply too much for most standard PCI-E cables. My guess is they are getting too hot and the PSU's thermal protection is shutting it off. If you feel the cables they are probably hot to the touch after the miner has been working a while. Each input to the S5 should be a separate cable. If the PSU has four separate PCI-E outputs you should be running a cable on each one.