I recently experienced this same issue. My processor would run at a constant 794MHz with a very high DCP latency. I contacted Dell support and after an hour of explaining the situation with a low level tech support person (who kept saying it was not a hardware issue but an issue with Win7 despite experiencing the same problem on Vista also) I asked for a supervisor. He agreed that it was a hardware issue and they fixed it in about 2 weeks (replaced the Motherboard, CPU, Heatsink, and Fan). Interestingly they left the BIOS at A17 instead of the newest A20 and came back with an Intel AMT/MEBx chip that it didn't leave with.
It has been running extremely well ever since.