Thank you very much both of you !
Your messages gave me the idea to test the camera itself alone, which is the first thing I should have done before Internet forums (sorry), so I put the lens back and yeah ! I've got a very blurry image but it's an image, the camera is fine !
For exposure and gain, I left everything as a default for a start, but I'll start to note them down now.
I'll have to wait for a little less sun to test again with the telescope and I'll try to focus on something far away and outside, I'll let you know !
Thank you again for your time, you made my day \o/