The dock went missing from the screen

I have a Mac OSX laptop. We were in the middle of a softward update. The computer said it needed to restart, which is normal, but when it came back on the entire dock was missing. Nothing works to get it to show back up again. Now, I cannot open any applications- it just says "cannot open... error occurred." I tried dowloading them again from our install disk- but the problem remains the same. One place I looked suggested installing again, but with the "archives option"- what is that? I couldn't find how to use that and so my install seemed not to work.