I have just upgraded my iMac from maverick to Yosemite following the instructions as given. When I turn on my mac desktop it asks me for my password so far so good. Within 5 secs of opening the desktop and before my wifi has even connected I get the legacy message saying I need to load java. I can neither do that nor go to the web site for more info Before the system shuts down again and reverts me to the user log on screen. I have a max of 10 secs before it does this no time to do anything before the java message appears ant the system shuts. I can do nothing whatsoever. Help urgently required.