You already know this, but I think for Service Desk it might be best to ask questions that reveal HOW someone thinks, rather than simply answering the question correctly.
Other softball technical questions you can throw out:
-User tries to turn on the computer, but nothing happens. What do you do?
-Outlook keeps asking for a username and password, what are your troubleshooting steps?
-A user's personal folders are missing in Outlook: How would you assist him/her with that?
-You don't immediately know how to resolve an issue, what resources would you use to find an answer, and at what point do you ask for help?
Love the last one.
With something that entry level I usually like to use questions that give insight into two things:
1. What they actually know.
2. What they do when they don't know.
With that said it really depends on what you're expecting out of them. To answer #1 I used to ask about how to join the computer to a domain, how to reset an AD password, a simple PST file question, ect.
Then a few questions that they likely wouldn't know the answer in order to see how they problem solve and handle the unknown. Random things such as: "You see a default gateway of 0.0.0.0 and the computer won't connect to websites, what should you do to resolve the problem?".
A user calls and says the restroom is out of toilet paper. Seriously, we used to use this one. It shows how a candidate will respond to an asinine question that has nothing to do with IT because as we all know, most people have no clue what IT really does. Modify it to your liking/HR policy.
Technical Questions should revolve around TCP/IP troubleshooting and local MS apps (Outlook, Word, Excel)
There's a bomb on a bus. Once the bus goes 50 miles an hour, the bomb is armed. If it drops below 50, it blows up. What do you do? What do you do?
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"When does the Narwhal bacon?"
If they have a puzzled look on their face, continue the interview.
If they answer correctly, end the interview immediately.
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A vital question is 'when does the day end' to many people have the 8-5 attitude and leave regardless if things are finished
Based on their resume, ask them questions you feel they should know. And, ask them questions that they probably don't know, as this will show some of how they think and react to unknowns.
My previous boss used to start off with something simple, tell me about yourself etc. Then ask questions on that or he would just read the resume and ask something related to what you have written in the resume. I asked him about that once, he told me firstly it puts them at ease and secondly if you screw it up it shows where you stand. For the record most of the people he interviewed got stumped on these.
My experience has been it not the question that is important its way you answer that tells a lot about the candidate. For service desk its not important if the guy knows AD or Networking its more important if that he knows where to find the information quickly, can do attitude or if he/she is willing to learn. Sometimes being too technical in a Helpdesk/Service Desk role is not good.
I remember the old joke where the interviewer asks the candidate "Whats 2+2" and he jumps up, closes the blinds and then whispers "how much do you want it to be!"