Help my laptop stuck in endless fixing repair loop

In computer terms I am equivalent to a preschool child. So I would appreciate an easy to understand answer as much as possible. I ran the window 10 installation last night on my Lenovo Y50 laptop. Today it is stuck in an endless loop of trying to Preparing Automatic Repair, diagnosing PCs and wanting to restart. I can't get past the limited choice of options to actually do anything useful. I just want to get rid of the thing and go back to Window 8. I am to computer stupid to know how do this. Please can any body clever out there help me using as little computer jargon as possible. I only recently got the laptop. I don't have a recovery disk.

Hi, first, this is not unique to Win 10- MS introduced this automatic repair in Win 8.. and when I ran that if my laptop experienced a thermal shutdown, I found myself in exactly your situation. So if you can boot up into Win 10, it's worth seeing how that runs for you.

Second- what to do (or what may work.. pragmatically).
Assuming your hard disk is ok and no significant corruption, try this:

Shut down. Remove battery.
Start up, and as soon as the laptop switches on, preferably before any disk activity, cut the power- suddenly- as in pull the cord out, flip the mains power switch.... (Yeah, I know...).
Now press and hold the power button for 10 or 15s.
Now reconnect power and try booting.

I've found ever since MS introduced this attempt at automatic repair (which has never achieved anything for me I can recall) if my laptop experiences a thermal shut down (gets too hot) I get into such a loop. That's the only way I've found out of it.

Otherwise you're into a repair scenario starting with chkdsk .... but try the above first.

I have had a few of those and i agree with the above, you got to do a hard shutdown , not sure about the other steps . I usually insert a repair disk because i have lost my boot options when i did a hard shutdown after a repair loop .

This happened to me too. I'm sure there are plenty of things that could cause it but in my case it turned out the order of my boot devices kept getting reset in the BIOS.

I updated the firmware on my Crucial SSD which fixed the problem after restoring the boot order.