There could be at leat a few possibilities 1 theres a bad connection on your battery terminals chack and make sure they are tight!
2 have you had your battery properly tested i.e are all the cells working! try another battery if you can get your hands on one to make sure!
3 check the terminals to the starter motor as this is a direct feed from the battery are secure and tight!
4 your starter motor could be jammed or the solonoid!
5 check your handbook for any relays associated with the ignition to see if they are working properly its just a case of elimination process im afraid!
ian mechanic
April 2009