Did you re-install from the CD or download file you received from Amazon in January 2014? If so, just go into Lightroom and go to the Help menu and one of the items (I'm not sure of the exact words since I am at work) is Update Registration or something like that. Select that item, enter your serial number.
By the way, very few problems in Lightroom are solved by uninstall/re-install. If the problem remains, you might want to state the exact problem in detail and perhaps someone here can help.