The WEP key should work if nothing has changed. Have you tried connecting the new laptop by ethernet cable first and then try setting it up wirelessly. Obviously you have made absolutely certain that the key has been copied correctly - O instead of 0 for example. The best way to ensure this is to type the key into a word document then copy and paste it when asked for the WEP key.
Surface Pro 4 UK release date, price and specs: Thinner, lighter, faster with new Type Cover and Pen