I just ended a render and I can't find the file. I don't choose any folder/location for saving it, I just rendered with the default presets.
Now there is a thing. I opened ANOTHER blender file and start to render too. Do you think the file overwrite?
Please help :(

Overwriteis enabled by default. You will need to re-render some frames at least, potentially all of one of them. – J Sargent Jan 09 '18 at 18:14