Having read your post I have some questions..

You write about a book "Business English: 100 business situations"

Do you mean

a) "100 topics for Business English Situations" by Amanda Cranedell Ju/

b) 100 Ways to Say it in Business English http://busyteacher.org/2638-100-ways-to-say-it-in-business-english.html

The school is updating their classrooms. One building is installing new desks and chairs.
Woww.. you have a building that can install desks and chairs.. Ripper place that mate...

One Friday, the maintenance locked all the computers; no problem as a student called the maintenance number listed on the counsole; he came in 5 minutes and opened the computer and we had class.
Whoooh it gets better and better there mate.

In one class, the projector was burned out; next class the following week it was fixed.
A miracle? did the building fix it or the maintenance?

My bonus? got it all, no problem, along with a spending cards from my department!
Gee you get credit cards there???

so if you need some excercise, you can go climb a beautiful mountain
Did you see any of the Von Trapps there?

Last question - are you a native English speaker? Because we don't "opened the computer" we would probably have a "locked computer unlocked"