While you only have Windows open (no programs... and if possible close anything you installed running in the background, like systray items or Norton), select all files in your C: drive (in Explorer), right click, go to Properties, uncheck "Compress this folder to save disk space". It will ask whether you want to apply it to just the folder or to the folder and subfolders and files. Do it to all subfolders and files. May take a few years to complete, and some files may not be uncompressed due to them being in use by Windows, but you'll generally have faster access to them.