Cpu @ 100%

  My PC, a Dell Optiplex GX280 (old but is meeting my needs) running Windows 7 Home, and using the Windows Task Manager, shows that lately the CPU is always running at 100%.  Looking thorough the Task Manager, it doesn't show anything using a lot of CPU resources.  When Firefox is running it is the highest at about 10%.  When I start the PC in Safe mode, the CPU usage only shows about 27%.  If I'm correct, Safe mode doesn't load all of the drivers.  Could this mean one of my drivers is at fault?  I haven't installed any new programs lately, just the usual updates from Microsoft, Nortons, Flash player and Java. 

  I've used Microsoft's Windows Sysinternals, Process Activity Summary, but I don't really see anything that should be loading the CPU.  The process svchost.exe > PID 1432, is showing some activity, but not a lot?  Is there a better program out there that can help me find out what is going on?