The first step in troubleshooting is to get the data. Here's some tools I suggest you:
1) MS TechNet Sysinternals Process Explorer to find which process takes so much CPU
There many setup possibilities with P.E. but I suggest you to try this column set:
- Process (mandatory...)
- Command line
- Start time
- CPU Time
- Network receives
- Networks sends
2) From the same, dowmload and install Autoruns (to know what started with Windows) and Process Monitor (for future detailed system checkup like tracing boot process...)
Warning: use Autoruns with caution. Don't disable or delete anything unless you really know what's you're doing.
3) Download and install System Explorer for security checkup.
The processes signatures/checksums are compared to the System Explorer database, There's many useful features but one interesting is the possibility to send any file, program, to VirusTotal...
4) Check the Windows services
You may start the services.msc but the best is to run mmc.exe and add services.msc in a personalized "console". (This keep your display setup for the next time).
You may find useful information about Windows services at the BlackViper web site.
Hint: some Windows services slow down Personnal Computers when they are not connected. as a workstation, to a Windows Server such as Server, LanmanWorkStation and LanmanServer.
I suggest you to stop these services if they are running and put them in manual or disabled (IF your PC is NOT connected to a Windows Server...)
Another useful tool is NirSoft's ServiWin (for services and drivers...)
5) Check if there is defective driver for devices with devmgmt.msc (or add it in the same "console" created for services with mmc.exe...). Check if there's yellow triangle, if so update the driver... If not: don't fix what ain't broken...
6) Update Windows and your applications. I suggest you to double check with the online Secunia's Online Software Inspector and set the option Enable thorough system inspection (Java must be installed to run these tests)
7) Preventive Maintenance
Check the s.m.a.r.t. data of your Hard Disk (there's many free
utilities for this: Piriform's defraggler or Speccy, SpeedFan with an
online s.m.a.r.t. check up, etc.).
IF the s.m.a.r.t. is "good" run CHKDSK to detect and fix HD and
Clean "TMPs" files with cleanmgr.exe (or a third party software BUT
avoid Registry "cleanup")
Uninstall all unused softwares, UNutilities or "bugaboo" programs
(alpha, beta, etc.)
Keep program loaded at startup to a minimum: in Autoruns check
Defragment the HD volumes
Check the PC temperatures (SpeedFan, Speccy, Open Hardware Monitor,
etc) and remove dust in your PC if needed...
Last words:Make a System Restore before any modifications (just in case).
Hope this help you to find a solution. Let us know. :)