Cgminer freezing with ant miner u1

[whtkrkid]

I'm mining on windows 7 with cgminer and one ant miner u1. Everything is working properly, but when it's mining after a while, I go and check on it and the computers frozen. I use NoSleep to keep the computer awake. When it freezes I have to hold the power button to shut it down manually. Please help!  Thanks.