Hi
First set Windows updates to, Download but not install updates.
Once it's caught up, (it will do it in the background and may slow your computer whiles it's doing it) chose which updates to install and do them a few at a time.
Next install CCleaner, and run the basic clean function and the registry checker.
Then in CCleaner go to Tools, Startup and look through the things that start at boot up.
Of the 44 things that would start automatically, I'm only running 11.
Keep things like your sound and video card utilities etc, turn off things like Acrobat Assistant and automatic updaters etc.
You can do this using Windows utilities "msconfig" but CCleaner makes it a lot easier.
And you can always turn them back on in the same place...