Render is black and dark

i dont know what happend but i made a model and every one hour i make a preview of the rendering’ and i dont know why but now when i am trying to render its not with color anymore. i have an presentation in 3 days and the model is dark /
what can i do? plz someone help me.

the first photo is in rendered mode and the second photo is in render preview
its something with this model because i tried to open the latest version that i saved before and it work. now i need to render the new one

i tried now to render it in high quality and there are materials but the shadow is very dark///

And your lighting is in place, and hasn’t changed since the earlier successful renderings?

Have you tried to add in additional lights, just to see if it generates changes in the dark shadows?