I'm using Windows 7 64 bit and I'm trying to resore a wallet using a backed up wallet.dat but it doesn't seem to be working, can anyone help?

Here's what I did

I installed a fresh copy of the Bitcoin app from www.bitcoin.org, ran it once, then closed it down
I deleted everything in the AppData/Roaming/Bitcoin folder
I copied wallet.dat to AppData/Roaming/Bitcoin folder
I started up Bitcoin again

It shows all my past transactions, but they all show "0/unconfirmed" and it shows my wallet balance as 0.00

What am I doing wrong? How can I recover my bitcoins from the backup?