What Pool, what OS, what CPU, and what temperatures? Mine runs 24/7 without problems.
I'm mining with win7 64bit, i7 3970k, temps are ok (60°), on nexusminingpool.
edit: i've just tried with cestballot pool, and it's working

thanks for your help!
That's the pool I use, I doubt that's the issue. I have 4 cpu miners running all the time without issue.