Hi Sonny, there are a couple of reasons your hypervisa could be turned off… in order;
You installed vm-ware on that system--- seriously they don't play nice together.
You moved (or changed the path to) the hdd where hyper-v stores its files.
Hardware failed--- this is very much a one in a million.
If it isn't one of the above then we need more info,
Is it the main hyper-v console or a sub-machine that stops working? For a sub machine, have you updated the cpu, network driver or antivirus because a new path through the firewall will then be needed.