PC light problems!!

[Twisted-1]

I just had a PC bulb burn out and when I put in the replacement it will only light up the very end of the tube where it plugs in. I thought the bulb was crap so I went to return it but it works fine in the store. What could be the problem? It is a 18watt 50/50 in my Nano. I have checked the fuse and its fine. Don't know what else to check.