ive come across this problem before.if u open ure door and face the edge of it.there is 3wee prongs on metal strip that slide up and down to lock door into frameif u work handel up and down check that they are moving.it might be the case ono of them is corroded and ceased work some 3in1 oil on the strip wd40 suitable for spraying into locking track .hope that might be helpfull.if alll else fails u can bye all parts if you have the year it was instaled and numbers .on lock
john
December 2007