White Screen Problem

Firstly, I am using a MacBook Pro from the mid-2012 range and running the latest version of Yosemite.

The problem I have been having is I keep getting the dreaded white screen when I boot up my MacBook. However, this is ONLY happening when I have USB sticks plugged into my USB hub. If I take them all out, the problem does not happen and the Apple logo appears on the screen and loads up normally. I have tried plugging in one USB stick a time and loading up, but the problem occurs no matter what. I take it that my MacBook is getting confused about where to boot up from.

I have gone into settings and made sure that my HDD is where things boot up from. I have tried reseting the PRAM several times as well. The problem remains.

What can be done about it?