Basically empty your recycle bin. For some reason on windows every time you create a new folder in your hard drive or do certain tasks on it Windows actually checks the files in the recycle bin. Don't ask my why but it does. So if you have a lot in your recycle bin, number of files seems more important than size, then this could be part of what's slowing things down.
It's rarely the only thing but any performance improvement is welcome isn't it.