go to your start menu, then 'run'.
Type in 'msconfig' and press enter
A box will come up, and there should be a tab that says 'startup'.
These are all the programs that start up when windows loads.
Untick all the boxes of programs that are not necessary, or dodgy looking. (don't ask me to explain dodgy looking!).
It will then say restart, you don't have too though.
If that doesn't work though, you might have some kind of virus/spyware/error, and might need to fiddle with the registry to get rid of it. I wouldn't advise that if you don't know what your looking for (not that I do!)