Check the outlet with a volt meter, you may have a bad ballast in there now, and it is supplying the wrong voltage to the light. Also try a piece of tissue of paper towel when you install the new bulb to keep you from touching it. You will not see the problem but the oils form your hands will cause localized heating.
p.s. If you don't know how to safely check the outlet with a voltmeter, find someone who does. It's not worth it if it kills you. you can always hire an electrician to come check it out for you.
