In reply to Blue Straggler:
There are quite a few things that can take up space without you deliberately saving stuff. To name some:
Temporary files
Temporary Internet files. Cached pages, cookies, etc.
Downloads folder. Each time you view a document online it could be sticking around in there.
System restore points. There will be something in the settings that let's you choose how much to let it use.
Scratch disk
System hibernate files
Windows logs and error dumps.
Redundant registry entries.
Yada Yada. 260gb used to be a big disk but the current operating systems are really fat bastards. Ccleaner is a good recommendation and you can sort everything above with it I think.