My wife has a Lenovo Yoga 2 ultrabook that often is very slow to boot up. It is currently running Windows 10, upgraded from Windows 8.1. The problem also existed under Windows 8.1.
Upon booting, the Lenovo start screen will show a circle of 5 dots, spinning in a circle. When things are slow, the dots spin very very slowly. It can take 10 - 15 minutes, or longer to finally boot up. Sometimes, the dots spin fast, then the machine boots up fairly quickly.
Also, this may or may not be related. To bypass the slow booting, I configured the machine to go to sleep on shutdown. If I close the lid, wait a few minutes, then open the lid, the machine comes up immediately. If I close the lid for the day, and open it in the morning, it does a full boot, which may, or may not, have the slow boot up. The same happens if I use hibernate to shut down. Apparently the machine is crashing over night while in sleep mode. I don't know why hibernate doesn't work.
If I check the even viewer after sleeping or hibernate failure, it will show a critical error saying that Windows was not shut down properly.
What can be done to see why this machine often (> 50%) boots up slowly?