the Dock being the bar of application icons by default at the bottom of the screen, rather than a hardware docking station?

there are many things that can cause this, surprisingly usually hardware, the Mac OS X itself being very robust. You wouldn't happen to have an external USB drive attached would you, or some other peripheral hardware thats recently been changed or upgraded? (apart from printers and stuff like that) Alternatively you might have a failing hard-drive, yes folks even Macs have all those same fun problems us PC users have, or possibly (but less likely) flakey RAM. However, with it being a MAC, you won't be able to fix it by yourself, you will have to take it to an Apple dealer and pay through the nose to have it checked out.

There are however various utilities you can d/l to check out where the problem is likely to be, offhand I can't remember all of them and I don't have my Mac cheat sheet to hand, but there is a good one called "Disk Warrior" that will diagnose your drive(s) for you.

The reason I mentioned external USB drives is that on Macs you can attach thesse by USB or Firewire but not both, and oncce set you cant swap it. However some drive manufacturers confusingly suggest that you can swap interfaces, and also sadly soem people attach both cable interfaces at the same time, just because the drive ships with both cables. Please tell me you haven't done that!