Invalid configuration information; please run setup program - help, what do I do?

I have started getting the above message "Invalid configuration information - please run setup program" every time I start my computer, a Dimension 4600. It also shows an August date in 2004 and 12:00 for the time. Each time, I click on F1 and everything continues normally, including restarts, but after a total shutdown, the same cycle starts all over again. Online suggestions are to make changes to the date and time in the BIOS, but I have no idea how to do that. I'm not particulary technical. Other comments are that the CMOS battery is probably in need of replacement, but if that's the case, I have no idea how to get to it or to change it, or if i do that, do I have to make other changes to the computer afterwards, or will everything just resume normally. Help!!!