I'm using Windows 10 Technical Preview on a Lenovo S540.
I had the same problem and I found a solution that worked for me:
How to fix it: Hold down SHIFT during the entire boot of the computer.
To prevent this in the future, disable the "turn on sticky keys by hitting SHIFT 5 times".
(for WIN10 TP: Control Panel\All Control Panel Items\Ease of Access Center\Make the keyboard easier to use)
Good luck!