When I turn it on it switches straight off again,

It may be something more serious,but the problem you describe is frequently due to corrosion on the battery contacts inside the camera. Remove the batteries and wipe the camera contacts firmly with a clean cloth (heavy corrosion buildups may require cleaning with a wire brush, steel wool, or sandpaper). Remove any residue that may have fallen into the battery compartment, clean the contacts at both ends of the batteries, and reinstall them in the camera. Assuming that the batteries are fresh/fully charged, this takes care of about 90% of the startup problems. I hope it works for you.