I have a late 2008 aluminum MacBook, 2.4 ghz, 4 Gb ram, 250 Gb hard drive, running Leopard 10.5.8. For almost a week now and with changes in the system or hardware, the computer is having a problem when coming back from sleep. If I'm working, close the lid, when I come back later, the computer does not respond, I get a dark gray screen, with no answer until the computer is shut off by holding the power button. Any idea?