I was thinking about my life all the day and I have a question I can't answer: Why am I so empty? If I'm talking to someone or doing something that time ago I loved... All is the same. I can't enjoy anything, I can't be happy or sad. I'm just empty. Maybe a bit afraid. I don't know what do I have to do. I want to feel happy, nervous, sad. I also want to cry. I don't know how to be alive again, and I'm tired.

Was there some event that caused your problem? For example, if you lost someone dear to you, or anything like that, properly talking about it might help. Cry your soul out, relying on someone's shoulder.
If life just started to become tasteless, I must ask you: Have you tried doing new things? Sports can become quite a big source of fun if you find the right one for you (unless, like in my case, there is no right one ._.) or just picking up some hobby?
For me, the thing that enables me to enjoy lifew is escapism. Pretty ironic, but the fictional world holds much more for me than the real one.
But before doing that, go out there, try to meet new people and new interests. This might be hard, but it takes some courage to start anew. Try out everything that interests you in the sligthest, from writing a book to mountain climbing, make an attempt to find new interests. If you still find yourself to feel empty, some private counselling might be necessary.

Just sleep properly at night, felling empty can happen when you're exhausted.