iBook won't wake

[Stephen Foster]

Our son put our dual 600MHz iBook to sleep but when he went to use it 
nothing happened. The number and cap lock buttons light up when 
pressed but that's the only sign of life. Tried re-setting the power 
manager but no joy, probably because the machine's not really "off". 
I know I've read about wake-up problems before but I don't seem to 
have saved any of the posts/solutions. Thanks for any help.
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"A man cannot step into the same river twice; for neither is it the 
same river nor is it the same man." Heraclitus c. 540- c. 480 BCE