SSD installation, strange behaviour afterwards

Il Mio Problema

I replace my optical drive with a SSD.

La Mia Riparazione

The installation was easy, no problem.

But when I install the OS on the SSD and boot from it, I can no longer enter sleep mode. I've tried to google the problem but have found nothing about that kind of behaviour. Anyone got a suggestion?

Il Mio Consiglio

Nope, installation was easy and the guide was good.