no keyboard, no mouse on startup

My mac mini starts up without the ability to use the keyboard or mouse. Quite debilitating. Before the first time it happened, I was getting a strange error message when trying to print. Does this suggest a USB hardware issue?
Does anybody have any experience with this sort of problem? Suggestions? Thanks

Have you tried another usb port? Do you have another keyboard to try? What brand keyboard?

There are four USB ports and I've tried all of them. I have tried two different keyboards.

Have a look at this link and see if the suggestions help you out:-

Apple - Support - Discussions - USB Port Problems ...

Thanks for the replies. I took it in, and the tech said the hard drive had some errors on it, and that it booted from an external hard drive. She also said there were some software issues, but couldn't really elaborate.