Sound Keeps Stopping

I'm currently running Windows 10 (directly upgraded from 7) on a Lenovo G780. The update in general has been a bit of a nightmare and I've had a number of problems, but now I'm having problems that I'm not even sure are related to windows 10 and my computer is becoming borderline unusable, which is a concern as I use it for work. I've updated all the drivers, and in fact I've managed to temporarily fix some of these problems only for them to come back again. These are the main problems I've been having:
 
- Start menu is only intermittently working, once it stops I have to restart to get it working again.
 
- Disk usage in task manager is often at 99%, and when it isn't it's still usually about 50%. Computer often crashes as a result.
 
- Sound keeps stopping, but in very strange ways. For example I'll be listening to music on itunes or youtube, and the music will suddenly stop, and the timer on the song will stop moving (rather than just the sound muting), it's as if the computer stops attempting to create sound. Again, this is usually only fixed by restarting.
 
- Computer sometimes won't turn off, for example when I shut it down from the start menu it starts closing all my programmes and then just stops without turning off. If I turn it off manually by holding the button, it starts up again as soon as I let go of the button. V strange. I've had to take the battery out a couple of times.
 
I've tried lots of solutions from people on the internet, I've scanned with Avast, Hitmanpro, Rkill, MBAM, Spyware, CCleaner etc. I've rolled back to before updates, I've then re-done said updates. I've done driver scanning software etc.