Does it feel any different from normal when you pull the release lever? If it feels extremely loose, then you probably have a broken or disconnected cable. If it feels about normal, then the problem is probably somewhere in the latch mechanism.
One way or another, this sounds like it might merit a trip to the junkyard. But start with a good spray of WD40 (or equivalent) down into the latch mechanism. It can't hurt.
2003 XS Premium MT >200k miles! ● 2005 Impreza 2.5 RS MT ● Robin-Subaru Powered Generator