Can I still publish a paper on peer reviewed journals several years after publishing it on ArXiv? I have done some discoveries concerning signal processing from about 6 years which I think are quiet important advances but I never have time to finish the works. As example I know that the main application are new on my field but I am not sure the theory does not exists on other fields. The links with other theories are not fully established yet, so I do not know exactly what is new and what is not. I do not want for now to be judged by peer reviewers which risk to only examine what is bad on the paper but I found it a pitty to not share those discoveries so I am thinking by submitting as preprint, and after some years and maybe some advices/correction from some readers, submitting it on a peer reviewed journal.

If I do that, and someone publish the same ideas after (particularly if they do not cite me, because they do imagine those ideas come from them or are obvious), will I still be able to publish it since reviewers can oppose me that those ideas are not new anymore ? Journals could not see the interrest of publishing works which are already known by the community on the only aim to help me to claim my anteriority. 

So to sum up, if a reviewer reject a paper because the ideas already exist from other works but those works are posterior to the preprint, can I ask to editor to not take this opposition into account?

Is there examples of important papers published years after their preprints? In that case should it be adapted to explain what others have done of your works ?
You speak of ideas, yet ideas are worth close to nothing without results, at least in the academic understanding. Sure, they are the beginning, but are not intellectually protected by themselves. Anyone can have an idea, but it takes work to develop that idea into a solid contribution to science.

So, if you have real "discoveries" and "important advances", you shouldn't be afraid to submit them for peer-review, as that is the only way to scientifically validate your work. Otherwise, it doesn't matter if someone develops on your idea and doesn't cite you. Similarly, it doesn't matter where you put those ideas, it could be arxiv, your personal website, facebook, etc.

As stated in the comments, you can submit a preprint and also submit to a journal, the preprint puts a timestamp onto your work so you have time to publish it (even if it gets rejected and you retry). However, this holds only for work that has the chance to get accepted for publication, i.e. has some real contribution.