What size HDD is it? 2.5 or 3.5"? Can you take it out of the caddy? Can you connect it into a secondary (slave) IDE channel on a desktop PC (with an adapter if required)?
Much easier to fix if you can get it to start!
Having said that, if you have any really important data, and it is worth several hundred pounds or more, DO NOTHING - just send it off to a data recovery company.
SD