Is there any external device connected to it and any message indicating that it is loading?
Is there any external device connected such as a usb, phone, etc? anything at all connected to the usb port?
When you reboot; does it show any options like BIOS, Factory Settings etc.. for the Function F keys?
What's the model # ***** this system?
No worries. I will opt out and open the question should you wish to come back later.
That is why i said that you can come back when you have time. This is going to take long to diagnose and troubleshoot it. There is no quick fix unfortunately.
Do you have any important data on this machine? The big mystery can be compared to a car whose engine has stopped working, without diagnosing it the technician or the mechanic won't be able to tell what exactly in the engine is causing it. Hope you get the idea.