That happened to me a couple times. Tried to scroll down to the end of
the log, and froze half way there. I can't use alt+f, nothing happens.
All I can do is Crtl+SysRq, then REISUB to re-boot. Or the power
button. The problem is affecting all types of hardware, processors and
video cards. 32 & 64 bit. Makes it difficult to diagnose. Trouble is
not everyone is affected. My wife's computer has virtually identical
hardware, and she is running 10.04 fully updated with no problems.