Thanks for all the help guys but I've sorted it out now. It was much harder than I thought it would be but I'll post my solution here just in case someone else has the same problem.
I'd read that I could program for finding rogue processes is Process Explorer. It's like Task Manager but on steroids and allows you to view processes that Task Manager won't show you.
I booted Process Explorer up and immediately saw that a process name Hardware Interrupts was using around 60% of my CPU power at any given time. I googled Hardware Interrupts and a few sites informed me that this process usually indicates bad drivers or hardware problems.
Learning this I went to device manager and systematically disabled each device and after doing so went back to Process Explorer to see whether Hardware Interrupts process was still hogging the CPU. I got down to Network Adapters and disabled my on-board wireless network adapter which I never use and will never need.
As soon as this device was disabled the Hardware Interrupts process shot back down to 0-2% CPU utilization and my computer is running beautifully.
Thanks for all the help regardless, it was very much appreciated!
- Nik
