I've found that some of the anti whatever software
can really slow things down. Decides it's time for a scan and nothing is going to happen for a while.
Have you tried using <ctrl> <alt> <delete>? Click on the processes tab and have a look. Bet you never realised just how many applications your computer runs without you knowing.
I do go through my <Control Panel> <add and remove programs> sometimes and if there's a program that I'm not using I remove it. Only remove those that I remember installing though.
Got to be careful as some of the programs do weird and wonderful but essential things.