Howdy JC LEON,
I am just a bit confused on what you are asking exactly. Are you attempting to load up a project that you have been working on or a project that you have downloaded from the Marketplace?
If it is a previously worked on project, you should be able to find it by either going into your library, found here:
or by launching the engine:
With both of those routes, you should be able to find all of your projects, whether they be from marketplace downloads or from previously worked on projects. Be sure that you are saving your projects so that you may reference them in the future. If you find that this information does not solve your issue, please let me know so i can further assist you. You can also place any questions on our AnswerHub, found here: https://answers.unrealengine.com/index.html.
Let me know if this helps any! Have a great day!