It is most likely caused from worn or broken parts. Just had to fix mine a few weeks back. Either the stricker or the latch get worn, maybe both. If you can get the hatch open inspect the stricker, it has a plastic piece around it. As it gets old it gets brittle and causes problems, you can order another from 50resto. As for the latch it is a bit more exspensive, so you may want to just try and clean and relube it yourself. I took mine off and used degreaser to help remove some of the old dried grease. Then you can use some white grease and WD40 or similar to lubricate it again. Putting in in a vice helps for this job. Then take a samll piece of pipe and push in onto the latch like it was in the car. Do this several times then apply more grease, it will help lubrication the whole latch.
As for reinstalling it you will have to take off the inside back panels. Crawl inside the hatch area and have someone or yourself slowly close the hatch. Watch where the striker and latch meet, they need to line up right in the center to work properly.
If you are having problems getting the hatch open (right now) you might be able to get at it from inside with a flat blade , but it will be difficult, good luck with that.