Dock disappearing, wallpaper flashing, mac lagging

[techwizard10]

When I booted my MacBook up today, I logged in and the dock disappeared. And the wallpaper started flashing. I don't know what caused this, so I went on the forums and tried terminal commands, and running Dock.app. Nothing worked. Cmd alt d didn't work either.
HELP!

 

[pmau]

My guess is your filesystem needs repair or your harddrive is dying.

External drives are really useful in these situations, because you need to be able to repair your drive without booting from it ...