When a Miele canister just stops working all of a sudden, it's usually a pretty clear indication that either you have a bad cord reel, or a bad switch. I would say that in 60% of Miele repairs that I do with this problem, the cord reel has gone bad.
One easy thing that you can try to see if the cord is bad, is put one hand on the on/off switch, and the other hand grab the cord (making sure it's fully retracted inside the canister). Now pull the cord out slowly with your one hand, while continously turning the switch on / off, on / off. Keep pressing the switch on and off while pulling on the cord. Usually if the cord reel has gone bad, then you may hear the vacuum attempt to start, or even turn on while you're pulling on the cord. The cord reels in Miele use a metal spring inside that makes connection with the rest of the vacuum. Over time this spring will start to loose it's strength, and eventually will get so bad that it no longer makes contact with the rest of the vacuum. By pulling the cord out slowly and pressing the on / off switch, a lot of the times the spring will make connection somewhere, and the motor may turn on temporarily.
If this happens, this indicates your cord reel needs to be replaced. I have done a detailed repair here on Fixya on how to replace the cord on a Miele canister vacuum that you may read here;
If you can't get the vacuum to turn on at all, this can only mean a few things. First the cord reels spring is gone completely, and wont make any connection with the rest of the vacuum, and you'll still need to replace it.
It also can mean that just the plug that plugs into the wall is bad, is your plug bent, or no longer straight on either prong?
It can also mean that your motor has gone bad. This however is usually the least likely of all the problems. The Miele motors are almost bullet proof, and typically last 20 years. I can count on one hand the number of Miele motor replacements I've ever done in 10 years of fixing vacuums.
I can try and help you diagnosis this further if my suggestions didn't help you. Please use the clarification request that you see here on this page to ask me a question. Please just let me know what happened when you tested the cord out as I suggested above. I really hope this was helpful to you. If you found this to be helpful, please be sure to rate the repair as helpful to you by clicking the thumbs up icon. I really appreciate that.