In attempt to get rid of some unneeded documents on my computer I tried to filter through my downloads to delete old downloads. I thought I was only deleting things that I had downloaded online, but apparently I deleted something important because now I can't change the desktop background. I already (and stupidly) emptied the Trash. I dont know what other functions have been disabled. I tried Repair Disk Permissions. And I can't find the plist screensaver thing. What do I do now?