Try rebooting. If that does not work then we need project and system and render details.
My render details are simple enough - HD 1080, AVI, "lossless with alpha". My system is handling the work just fine, after my recent upgrade. But everything was same-same from the project just yesterday. The difference was that, today, when I clicked "render" after queuing the project, it just sat there until I finally gave up. And the project was a simple opacity change of some text.
I haven't rebooted. Should have tried that first. At present, I'm re-installing. Once re-installed, I'll reboot as well, of course - and then let you know.
Just a heads-up:
Either the re-install or reboot worked. Don't know of course, because I didn't follow the standard trouble-shooting method of simplest first. A reboot might have sufficed.
If it happens again, I will try that first - install second.