I was researching the issue you are experiencing and came across an article that I feel would be helpful in isolating where the issue is happening. It is called Isolating issues in Mac OS X found here: http://support.apple.com/kb/ts1388.
You want to start here and work your way down if needed.
Is it a software or hardware issue?
Pay attention to important clues.
- If the issue seems specific to a certain application or Mac OS X feature, troubleshoot software before hardware.
- If the issue occurs as the computer starts up--unless the computer does not turn on at all-- troubleshoot software before hardware.
- For other issues, or when software troubleshooting does not produce a resolution, use the rest of this document.