Laptop won't turn off after request

Hi,
I've upgraded to 22, thanks a lot !
That said, when I want to turn my laptop (Lenovo Thinkpad P50) off, the screen turns black but the light under the keyboard keeps turned on.
No key would turn it back into action, I have to press the ON/OFF button for 6 to 8 seconds to definitely turn the computer off.
Any idea ?
Thanks,
ZaamsK