CPU overload, and distorted playback

While using pro tools 10, I get a CPU overload error message often, and distrtion on playback. The issue can be temporarilly fixed by changing the processors in the playback engine, but it is only Temporary. Usually does not get me through a whole session. There have been many posts on here about this problem, but no final solution ever seems to be determined. I have an I7 processor, 2 hard drives, and 8 gigs of RAM. I record onto one hard drive and run pro tools off of the other. This could not possibly be a hardware problem. Please Help…..