Call it writer's block, call it hitting a brick wall. Whatever you call it, it's every writer's nightmare when the words won't come and writing anything is an effort.
Here are some things I do you might find useful:
1. Stop at a question - is your character pregnant/dead/the killer/in a building that's about to collapse - leave your character on a cliff-hanger and you will want to know how that question is answered.
2. Leave your character in peril. They could be facing a gunman, about to fall down a cliff, be in a stolen car escaping from the cops.
3. Suggest characters are not who or what they seem to be. For example, the police come to protect your family in peril, but it becomes clear they are not the police. This is a good plot move as it leaves a question - if they're not the police who are they and what's their motive.
4. Follow Stephen King's advice. Think about what should logically happen next. For instance, I have a character who's been manhandled into a van by 2 thugs and taken to a deserted location. She's saved when one of them turns out to be an undercover cop. My character didn't see it coming and to be honest, neither did I.
5. Write something ese. It doesn't matter what it is. This can get you writing again.
6. Watch something funny. You might find laughing inspires you.
7. Do some unusual research. I knew that I wanted my Kirsty character to jump out of a cake but when I tried to write it, it was dreadful. I did the research and it really helped me with the writing.
8. Ban yourself from writing anything at all for one day. There is nothing more guaranteed to make you want to do than telling yourself you can't.
8. Ban yourself from writing anything at all for one day. There is nothing more guaranteed to make you want to do than telling yourself you can't.