My iMac was acting up so I powered down to reboot. Note I could not access the power down/ restart option from the apple menu so I had to hold down power key. When I rebooted I logged into main account and there were no icons on the desktop. I could not open apps from the dock, nothing worked. Couldn't even power down from the menu. Restarted again holding power key, same thing. Restarted again but this time I logged into a guest account which worked fine. Logged out, logged into 2nd guest account no problem. Logged out, tried to log into main account same issue as before. Help?!