It says I have to fill in a password which I do but it says 'Incorrect password!'.
Did you originally setup a password? If so, it sounds like you haven't put in the correct password... CAPSLOCK maybe?
If you never set up a password when creating the wallet, you *might* have an old wallet laying about... click the "Choose..." button to the left of the box with the wallet name and see how many wallet files it displays.
I've wrote down the 12 words when installing the wallet. What am I doing wrong and how do I get access to my wallet via the 12 words?
Just create a "new" copy of your wallet... on the screen asking for the password, just enter a completely different wallet name... like "recoveredWallet"...
It'll go through the new wallet wizard... select "standard wallet -> I already have a seed"... put your 12 words.
It should recreate your wallet and you should see the same addresses and the transaction history.
