I can't open new projects + errors in re-opening old projects

When I try to open a project file I get a message telling me: missing (game name) modules the following modules are missing or built with different engine versions, Would you like to rebuilt them now? if I press I get an error message. a similar problem occurs when I want to start a new project, instead of opening the editor I get a message telling me that the editor hasn’t started but anyway I can go to visual studio, how can I solve these two problems? Thank you in advance !!!