Booting in safe mode skips many extensions. If Safe Boot resolves the issue, this implies a Startup Item or Login Item is the cause.
Before you start any troubleshooting or System or hard drive maintenance procedures, it is important to BACK UP YOUR DATA to other drives or CD or DVD media. This is important because the problem may be that the hard disk may be hanging on by a thread and the most basic procedure may lose the drive and data forever. ''If there's really PITA to recreate data make TWO BACK UPS.''
Take a screen shot of the Startup or Login Items you have defined and save the list to the top or shared folder of your HD.
While in SafeBoot create a new account. Set to log-in to that account or choose it at startup. Restart. If all is well your problem is a specific Startup or Login Item. Enable one item at a time from your list until you encounter a problem. Use that solution to fix your original account OR transfer your old data to the new account.
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