I recently upgraded my Snow Leopard to Mavericks because of major problems encountered with Snow Leopard. Everything was working well in my Admin user account and in the Guest User account, until earlier this week. Suddenly, the Guest User account is opening very slowly, and the Guest desktop GUI won't work - Desktop appears but the GUI is screwy, The Dock only shows 3 of what should be about 12 icons on it, but when I move cursor over the Dock, only the names of all the apps in the Dock appear. But none of the apps in the Dock will run when I click on them, or Control>Click on an apps name and then click on Open. Actually can't get anything to run from within the Guest account, including Safari and Finder. System Preferences menu opens, but very slowly. Everything seems to look "normal" in System Preferences?! I should also mention that, while I was in the Admin user account, and at abut the same time that the Guest account problems cropped up, the 3000+ songs in my iTunes Library suddenly disappeared. The iTunes Music library folder was almost totally empty with only 4 songs in it - but iTunes still showed all the info for all 3000+ songs in it's library window!! I fixed this by restoring all 3000+ song files back into the empty iTunes Music library folder, from my recent backup. But why did my iTunes music files suddenly vaporize?! And last but not least, the computer generally seems to be running slower than only a couple days ago. I have the AVG anti-virus app that scans my iMac every day. I went through a lot of headaches when my Snow Leopard started acting weird. But it's behaviour was quite different from the odd behaviour I'm seeing with Mavericks. Someone suggested I do an SMC reset, but I don't have a clue what that is or how to do it - don't see any mention of SMC in any books I scan at my local library. Any thoughts, please, on all this sudden weird behaviour from my new Mavericks system, and how could I return the Guest User account back to normal "health" without having to do a full clean re-install of Mavericks?