I have an imac 27" late 2012 running OS X 10.9.1. Have a trouble as it doesnt not come on instantly from stand by. The screen takes around 20 seconds to come on (it used to be instant) and is wehite (but shows my desktop in the back ground). A bar timer then scrolls for aropund 10 seconds as if it is searching and then the mac starts up. Has anyone else had experience like this?