imac 10.6.8 Problem

Hello! My imac 10.6.8 was getting very slow, so I followed some advice on how to speed it up, by deleting unwanted stuff. I must have deleted something important because I have lost my Time Machine firewire backup drive icon on the display, along with another external drive on a USB connection. If I do a restart, the icons show for about 3 seconds, then do a slow fadeaway. The drives show up in Disk Utility where I can do a verify, and repair.