Ok lets try starting in the Mac up in 'Safe Mode'...
To start up into Safe Mode (to "Safe Boot"), do this:
Be sure the computer is shut down.
Press the power button.
Immediately after you hear the startup tone, press and hold the Shift key.
Tip: The Shift key should be held as soon as possible after the startup tone but not before.
Release the Shift key when you see the gray Apple and progress indicator (looks like a spinning gear).
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What is Safe Boot, Safe Mode? (Mac OS X)
Safe Boot is a special way to start Mac OS X 10.2 or later when troubleshooting. Safe Mode is the state Mac OS X is in after a Safe Boot.
Starting up into Safe Mode does three things to simplify the startup and operation of your computer:
It forces a directory check of the startup volume.
It loads only required kernel extensions (some of the items in /System/Library/Extensions).
It runs only Apple-installed startup items (some of the items in /Library/StartupItems and /System/Library/StartupItems - and different than login items).
Mac OS X 10.4 Tiger only: It disables all fonts other than those in /System/Library/Fonts .
Mac OS X 10.4 Tiger only: It moves to the Trash all font caches normally stored in /Library/Caches/com.apple.ATS/(uid)/ , where (uid) is a user ID number such as 501.
Mac OS X 10.4 Tiger only: It disables any Login Items.
Taken together, these changes can work around issues caused by software or directory damage on the startup volume.
Some features don't work in Safe Mode
Safe Mode can be useful for troubleshooting. However, certain Mac OS X features do not work when you are started up in Safe Mode. For example, you can't use DVD Player, capture video in iMovie, use an AirPort card, use audio input or output devices, or use an internal or external USB modem.
Give this a go and we'll take it from there...
regards
Ric