FOB (second one) doesn't work

I just bought a 2000 convert and the second fob doesn't work. Replaced the battery and tried to reprogram it according to the owners manual but still nothing happens. How do I know whether its already been programmed for three remotes. How would I start over to program them all. The second remote looks brand new like it has never been used. Any way to tell whether to buy a new one. Should I take it to a dealer?

thanks Marv

When I purchased my car last month the fob didn't work either. I had to go to Chevy and buy another one and have it programmed. I had them check the old fob while they where programming the new one and it was no good, so to make a long story short you might need a new one.