Here are the steps you need reinstall the Apple Extension Manager (if necessary), and test for extension conflicts.
Step 1
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Open the Control Panel folder located in your System folder.
Step 2
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Find the Extensions Manager control panel. If you cannot find the Extensions Manager control panel, look for a folder inside your System folder called "Control Panels (disabled)".
Step 3
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Launch the Extensions Manager
Step 4
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Either write down all the items with a checkmark next to them, or use the Save Set option in the Sets menu to create a temporary set.
Step 5
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Choose System 7.5 Only or System 7.5.2 Only from the Sets Menu.
Step 6
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Close the Extensions Manager (at this point the Extensions Manager will move all non-System 7.5 Extension to the proper disabled folder.)
Step 7
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Restart your Macintosh computer.
At this point your Macintosh computer is using only System 7.5 or System 7.5.2 extensions.
Step 8
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Test your Macintosh. Verify that the problem does not reoccur with only System 7.5 extensions running.
Returning Your Previous Extensions
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Step 1
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Open the Extensions Manager
Step 2
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Either select the extensions and control panels previously installed, or if you saved a temporary set, choose that set from the Sets menu.
Step 3
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Restart your Macintosh