Inconsistent connection to router - PLEASE HELP

I bought an Inspiron 9300 notebook a year ago. At the time I could connect to my wireless network (located two floors below) with ease. However, over the last two months things have become very inconsistent. Often my wireless card does not even pick up the home network - when it does though things usually work great. What is going on? COuld I have a defective wireless card or is something else at work here? Any and all help is appreciated.