Those latches can real rust up or even bend so take a good look at the latch on the hood, spray it/soak it with something like wd40 while moving it back and forth rapidly.Then have someone moving the hood release latch handle back and forth while you soak the mechanism and the cable fully then keep trying it see how it works.The cable maybe stretched or rusted and may require more then just a good cleaning.lubrication it may need to be replaced.
Hope that helps and best of luck.By the way soak them several times and also allow then spray to soak in over night bec I find letting it soak for awhile and doing it several times usually helps especially if using products like wd40.Sometimes you need to bend the hood latch back in-line a bit bec it can tend to become bent naturally over many years.