I have a floor lamp. The dimmer knob controls the brightness as well as turning it on and off.

It still works with regards to turning it on and off but it no longer works to control the brightness. I figured it was an easy fix but the hardware store was no help.

Anyone know what might be wrong and what I need to buy to fix it?

A lamp store would be a better place to look. Knowing the who made the lamp might help. Information on the switch itself might help with an internet search.