If your vehicle is showing hood won't pop open when pulling the interior release lever, here are the most likely causes and the parts you'll need to fix each one.
The latch mechanism at the front of the vehicle is exposed to road grime and moisture. Over time, lack of lubrication causes the moving parts to bind, preventing the spring from popping the hood up when the lever is pulled.
The metal cable connecting the interior lever to the front latch can stretch out of specification or snap entirely due to age and repeated tension.
The plastic handle inside the cabin can become brittle and crack. When pulled, it flexes or breaks instead of applying tension to the release cable.
Often occurring after front-end bodywork or a minor collision, the latch and the hood striker may not line up perfectly. This causes severe binding that the release cable cannot overcome.
On vehicles where gas struts provide the upward pressure to 'pop' the hood (rather than a latch spring), completely dead struts will allow the hood to unlatch but not lift enough to clear the locking mechanism.