Render never finishes, and then stager "semi-freezes".

I've been trying to render a file for 2-3 days. I set it to render, then leave it. When I come back, hours later, the render hangs somewhere in the middle of the progress bar.

My scene a big canvas with lots of objects. 

I'm rendering 4000x5000 px. 

I don't need super high quality, I just need to get this thing I've been working on for weeks over to photoshop, in one piece. 

Since Stager isn't presenting any errors, it's just comatose, I don't know what to do. The interface "works", that is I can go through the save dialogue, but it just doesn't save anything.

It may be that the underlying process is just busy, but... when nothing happens, nothing keeps happening, it's really hard to figure it out. 

When I come back, even if I leave it for an hour after that, the progress bar isn't moving.

Also, since it's not the app crashing, only the underlying software, there's no crash reports, nothing like that.

What do I do?