What other activities is your computer doing at the time? I suggest running
Process Explorer to see what is executing at the time. On my computer there is a svchost.exe running a service dnscache that will basically max out my cpu and then nothing else runs. With process explorer I can suspend it and resume later, although then I can't surf because the browser needs this service. It seems Microsoft bought out the program in July but hopefully you can find it from the link above. (procexp.exe, procexp.chm (help file))