On my 2000 XJ, I tried to open the hood but the latch was very stiff and only one side would pop open. After pulling the latch many times I could pry open the hood from the side that opened.

What could the problem be?

 

The one lock mechanism is probably stuck.

There is a rod that connects the two locks. If you can get the hood open enough, grab that rod and give it a pull. It will probably be difficult, but hopefully the second lock will actuate.

Once the hood is open clean and lube the entire system.

 

Get rid of the awful factory cables and put in hood pins, I paid $14 for mine and it took me an hour to install. I like the way it looks too makes it look more utilitarian. I tried lubing mine up but the actuators kept freezing up and eventually the cable broke.

 

I'd try lubing everything nice. Sometimes I use spray chain and cable lube. It really shoots out, you can lube your hinges from across the street!