Sorry to be blunt but I had the same problem and the brushes on the starter have gone. You need a new one, they're about £60 on exchange policy of your old one. If you're mechanically minded and have decent tools, it's not too hard. If you're not experienced, don't even bother - it's more hastle then it's worth, believe me!
1994 laguna 2.0 RT, November 2005