I just had another annoying problem with my MacBook Pro 4.1, running Mac OS X 10.5.6.
I left the machine unattended for like 10 minutes or so, and when I came back the screensaver was active. Sliding a finger over the trackpad wouldn’t produce the log-on dialog, nor would pressing keys on the internal keyboard. The machine was not crashed, however, since the screensaver animation was still running. What was even more strange is that the “Power on/off” button would work — when I shortly pressed it, the log-on prompt would appear.
Fortunately my view fell upon an external USB mouse, which I immediately tried. Voilà! I could move the mouse pointer with the external mouse, but the trackpad and internal keyboard were still dead.
I then attached an external keyboard, and that one also worked.
Back in Mac OS X I stopped all running applications, and restarted the MBP. Afterwards, all was fine again.
What the heck is this??? I thought Mac OS X was famous for its stability and reliability?! Is that what makes it “superior to Windoze” (according to a considerable fraction of Mac users)???