About 15 minutes ago my MB locked up and the screen turned dark blue. I turned it off and then pressed the power button to turn it back on yet almost instantly I see a white screen. Nothing else happens. Edit: just to add, it takes a about 5 seconds for the hard drive to start spinning; it then appears to slow down after a minute or so. It acts like it is waking from sleep rather than actually loading the OS, even if I take out the battery. It has been running for the last few days pretty much constantly (via mains) so maybe it just over heated? Any ideas what could have caused this? Thanks. Help always appriciated.