If anyone can help... I bought my sis and her husband an iMac in 2010, and now it's acting up, so I am on the hook for 24/7 tech support. Anyway... It's a 20" iMac, intel based. Recently upgraded to Lion, but was acting up a little before then. When the computer starts up, there is a brief message that the startup disk is almost full. It has a 500 gig hard drive. They only have about 60 gigs of pics, music, etc. on the disk, and nothing else that I can see on the drive BUT the drive says about 499 gigs are used. I do a command-I on the main folder and it shows the 499 gigs used, but if I look at all the sub folders, they only add up to about 60. They have been running Time Machine hooked up to a 320 gig external hard drive. The last backup that went through was in December. Since then, it has been trying to back up and failed because it says the external drive is also full. So, does anyone know how to find which files are hidden? Is this a Time Machine problem keeping hidden local files since the external filled up? IS something else writing to the hard drive and filling it up? I've run the disk utility, the disk checked out as OK, verified and repaired permissions, etc. Also, when I go to "About this Mac" and click on storage, it shows 450 gigs filled up with files labelled "Other." The only thing funky they ran was AOL Desktop, which now won't work after upgrading to Lion, and I deleted it. Any help would be appreciated!!!