Can only wake MacBook Pro up from sleep with power button?

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My MacBook Pro can only be awakened from sleep mode by pressing the power button. Other MacBook Pro's I have used can be awakened by touching the mouse track pad. How do I change this setting so I can wake my computer just by touching the track pad?
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I agree with the comments posted but this is not my problem. here is a further update.
If I close the lid on the MBP and it goes to sleep then it can be awakened. If it is connected to the 23" Cinema display and it is put to sleep in this way then it can be awakened. If it 'goes to sleep' itself when connected to the display (despite sleep being set to never) then it won't awaken except with a power on reset. If the display is disconnected then the MBP never sleeps ie it obeys the power settings.
Have tried reset pram, power management reset nothing works. Am on latest 10.4.10 update. This only started happening recently and (I think) after .10 installed.