I submitted a paper for an Elsevier journal in which the acceptance deadline appears as the 5 of may. The problem is that when I enter into the author´s menu it appears that my paper is with the status Required Reviews Completed and it has been like that for more that one month. Does it mean my paper has already got rejected? what should I do in this case?
Contact the editor and ask about the status of your paper.
Does it mean my paper has already got rejected?
No, that's not what "Required Reviews Completed" means...as you probably know. Maybe your paper has been or will be rejected and maybe it won't: there is no point in guessing.
what should I do in this case?
Do what one normally does when one's paper is rejected: take the feedback into account and decide whether to resubmit elsewhere and whether to revise your paper.