Your sentence is OK. But "off" is not a preposition there. It is an adverb.
Student or Learner
May I use the preposition "off" in the next sentence?
"The computer network has gone off so I can't send any emails this afftenoon."
Computers and networks usually go down, not off.
That's true, Dave, but I believe the down is more metaphorical than off. Off comes from the traditional phrases switch off / switch on.
I think to answer denismurs initial question, it's "yes".
(If the network is down, then something has switched off, or been switched off, hasn't it?)
Ok. "Go down" is more colloquial.
Yes, I've understood from the exercise that there had been a failure which led up to disconnection of the network.
I see you have done some other posts about similar preposition questions, denismurs. As TheParser said in one of the others, they can drive you mad. I think it's true with many prepositions.
When I was a teenager I used to get Idiom Tests from my German teacher as well as vocabulary tests. It was a great idea!
If you like this kind of thing here's a good example. In BrE we say in the plane/ on the plane/ in the train/ on the train/ in the boat/ on the boat/ on the bus/ in the car, But if you said "I'm going on holiday on the car, they would think you were clinging to the roof rack.
Why? Nobody knows. Often there are no rules. There are so many ways of saying things that you just have to learn eventually. Just keep trying them out with experienced English speakers!
'Go off' sounds like either an explosion, or a timed countdown.
Wear short sleeves! Support your right to bare arms!
I'm one of those people who refer to a long list of words generally as prepositions (on, off, under, above, in etc). For me, "to go off" is a phrasal verb and, again for me, that is something which consists of a verb plus a preposition. Verb = to go; preposition = off.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.