My iBook G4 runing mac OS X is not displaying the dock(thing which pops up showing whats open etc). I can not move any item around the desktop nor can I delete them or open a menu via right clicking. I cannot shut down or reset using the apple menu, or using the menu that pops up if u click the power button. If i turn up or down sound/brightness all that appears is a white patch over where the sound/brightness display should be. I can force a shutdown by holding the power button or taking out the battery, but these are the only ways. All items on the desktop can be opened by double clicking them, they can all be highlighted, just not moved at all. I cannot shrink down firefox using the orange negative sign(top left). Pressing alt+tab doesn't show which programmes are open, or allow for switching between open programmes

Sounds like the Dock and Finder are hosed. I'd boot from the Install DVD, go to utilities and run Disc Utilities. Repair the disc and permissions and restart. If that doesn't do it I'd wipe the drive and reinstall OS X.