Hard Disk C is nearly full

I dont know if ive come to the right board but my girlfriends laptops C drive is almost full but cant see exactly where or what the large files are.

Strangely the c drive is nearly full at 288gb but when i click in the folder theres nothing of that huge amount.

I unhide files but still cant see where the the over load is coming from so it can be deleted. She has a vista.

I hope someone could help please.

Thanks

 

There's a little program I use called SpaceSniffer v1.1.4.0 available here. It's a standalone product that doesn't need any installation. Right click it and run as administrator.

 

Super that was great help and figured out the cause. It was a file called treestate.dat which was related to realplayer. Thanks again, cleared up some other extras.