I used to have the same problem when using Genoil miner. It is very CPU intensive in the first few moments / minutes (depending on CPU) as it loads the DAG. However, once it's loaded there is no problem. I had to upgrade my CPU a bit because the cheap CPU I had could not handle loading the DAG and the rig would restart.

Just as a side note. Genoil has stated he is not actively developing this miner any longer. It was kind of unstable when I used to use it, and I'd recommend switching to one of Claymore's latest miners or something else for better stability. If nothing else, faster miners have been developed since Genoil stopped updating his.

Having said that I used Genoil's miner for the longest time and appreciate the work he did!