Maybe you need more rest. Take some time off and work your brain for a while.
Read some good books, like Mike Mentzer's High Intensity Training.
Learn why your time off is just as important as the time you put in the gym.
Get a good anatomy book to help you change your routine. Maybe you'll be surprised to find out how many times a week you're over-training the same muscle.
Re-evaluating your workout once a month, or so is a habit that I think everyone could benefit from.