Missing Explorer in Windows (Windows Vista, 7 and 8)
This document shows how to restart the explorer.exe process. The symptoms of a terminated explorer.exe process are missing start menu and desktop icons.
A screen without an explorer.exe process might look like the one below. It may however include some windows that are not minimized, but it will definitely be missing a start menu along with desktop icons.
Press Crtl, Alt and Del all at the same time. This will bring up the screen, like the one below, where you can start your Window's Task Manager. Go ahead and click Start Task Manager
Then click on File and then New Task (Run..)
Type into the open: form explorer.exe and then press OK. It may take up to 30 seconds, but your desktop and start menu will start to load at this point.