CPU 100%

I maintain several computers for a small business: One system inparticular has had issues with CPU usage between 80-100%. This usually occurs during the first 5 minutes of start up then will go back to 0% for a short time. Without doing anything, just watching the CPU usage, it will jump from 0% to 17% to 53% to 97% to 100% and wobble between 97-100%. I watched the processes and one of the svchost.exe jumps between 59-99% during this time then will just stop. Is there a specific problem I should be looking for? I have tried msconfig, add/remove programs, spysweepers and even checked physical connections on the motherboard. Any help would be greatly appreciated. Thank you in advance.