I would start off by trying to identifying the process which is causing the CPU utlisation
Go into task manager (Start->Run, taskmgr.exe) click on the processes tab and click on the CPU column a couple of times. The image name will be the process running with the highest utilisation.
A couple of other ideas
Have you scanned for malware using something like malware bytes or Lavasoft Adaware?
what process is ocupying cpu..svchost?