You're going to have to give a lot more detail of your problem.
Ostensibly, the OS is supposed to at least go to sleep when idle for some time. At first glance it sounds like situation normal, but the fact you post indicates that's not the case.
Secondly, it isn't clear whether the system is sleeping vs. shutting down (there is a difference).
Third, you have no indication of time - is this after minutes? hours? that plays a factor too.
Fourth, you've 'tried all the suggestions', but don't indicate what they are - we have no idea what you've done right now.
So, more details please.