i've been getting an error screen where my desktop is greyed out and a warning appears telling me to either hit the restart button or hold the power button for a few seconds. i've been troubled by this a few times; twice when i was trying to install parrallels, once when i unplugged my cellphone without ejecting the port, and once when i was trying to play an avi file on vlc player. has anyone else got this problem? does anyone know what's the matter? should i take my mac pro back to apple? i'm just worried that this might turn into a frequent issue. thanks in advance.