USB Keyboard doesn't work after sleep

Hi,

I've recently bought my first mac mini and I'm having some issues when it goes into sleep mode as both the keyboard and mouse don't seem to work after the computer goes into sleep mode - is this something I can somehow resolve? I've got the latest OS (10.11.1) and all app updates are applied.

I basically need to long press the power button to fully shutdown before I can actually get back to work.

Is there something that I can do to fix this?

Thanks,

cveiga