Strange problem. 2009 Mac mini 2.0GHz, Mac OS X 10.7.3 (fully up-to-date). I cannot rearrange my desktop icons. When I try and drag them, there is a white "not allowed" ("no smoking"-style) symbol beside the cursor while dragging. I just noticed now that screenshots no longer work via the keyboard shortcuts, either -- the snapshot sound occurs, and no file appears on the Desktop. Permissions, repaired. Disk, checked and validated. Computer, rebooted. User account, logged in and out. This problem has existed since 10.7.2. I never realized how little I rearrange icons on my desktop until I no longer could. Help?