Okay this is weird, I had this issue a while ago but it never came to this. I have bootcamp and want to change OS, so I restart while holding option key and here are 2 outcomes: 1. The screen stays grey and mac is just standing like this, I waited for 5 minutes but no options came out. 2. If I hold option immediately while Mac is restarting screen stays black and sleep button is lid up all the time, nothing happens. Anyone knows how to solve this issue?