System restore is too obvious, but quite sometimes it helps and quite often we see users (not you) forget about it.
Just an article here:
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Some quotes:
Disabling Network activity before sleep Terminating all network activity -- in some cases necessitating a power-down of the AirPort card or disconnection of an Ethernet cable -- is, in some cases, particularly effective at eliminating the "blank screen on wake-up" issue.
Do not connect, disconnect external devices during sleep Avoiding disconnecting or connecting external devices -- USB, FireWire, etc. -- during sleep eliminates this issue. It also appears that, in some cases, all external devices must be disconnected
before putting the machine to sleep.
Checking for Bad RAM Faulty RAM may be the culprit of your Wake-from-sleep issues -- especially if distorted video is present.
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Turning off all Wake/Other options in Energy Saver Some readers report that turning off
all special automatic sleep options has resolved this problem. This can be accomplished by entering the Energy Saver pane of System Preferences, clicking on the "Options" tab, then unchecking all options, including:
- Wake when the modem detects a ring
- Wake for Ethernet Network administrator access
- Restart automatically after a power failure
Close the lid again and wait In the case of some PowerBooks, simply closing the system's lid, waiting a few seconds, and re-opening the PowerBook allows proper wake-up.