Help!

I've been pulled into an interview tomorrow to ask some "techie" questions. The job is to support our web based solution for end users who have issues. I've been asked to come up with some technical questions to ask the candidate. I won't see the resume until 9am tomorrow, the interview is at 10am. I'm just looking for some very general stuff to ask to see if he/she can think fast.

Anything you can add would be much appreciated as I've not had to do this before.

I'm thinking of the following:

An end user has an urgent issue where they can't get to their online data, you've not seen this issue before and don't have an immediate solution. How do you advise them?
Looking to see if they can think on their feet.

A user complains that they can't download a file as the disk is full. What could you advise?
Basic PC knowledge.

That's about all I have at the minute, I've not had to do this before and I don't want to ask anything "stupid".