They're all correct, you didn't give us much to go on, but I know it's because you're frustrated.
let's start with the basics-you've connected the converter box to your TV and antenna (it must have an antenna). You've followed the set up directions, scanned for channels and now all you get is a black screen that says "no signal". If you're not getting the 'no signal' message, then either you haven't done the set up correctly or the box is defective.
If you are getting the no signal, then you need to either adjust your antenna or get a new one. even though 'they' say your old antenna will work, it doesn't seem to be the case more often than not. And a lot of stations when to UHF in the conversion.
I like www.tvfool.com for finding out what stations you'll get and how far away you are from them, the direction they are and what interferences might be in the way. These are all things to consider when shopping for a new antenna.
I was so frustrated that I spent the time to research antennas and find the best ones (short, medium and long range) at the most reasonable price. I made a blog a bout them...