You just may need to change the battery, 2 x CR1620 batteries (£1 from ebay) and then resynched it (in the manual it will give you instructions on how to do this) - this is what I had to do recently.
If you have to get a new fob and blade, either ebay or dealer for the parts and then the dealer to get it cut and resynched. You should have the keytag that came with your keys that hold the cutting and transponder information - without this it may be tough I believe.