I found a method that I think that works. It's for get confident and relax (without drink alcohol). The method is: record my voice telling me good things that I did, in this case related to repair computer like:
-The PC turned off when it started a game and I found that the CPU was a little loose (this was the cause of the problem).
-The PC had a problem with the DVD drive, it did not open. I found the solution, I applied 3 in 1 oil in a piece and it worked.
-The PC did not turn on, I checked the power supply and tried with other. It was the solution.

When I'm going to feel bad, I will try to apply that method, to feel better: confident and relax.

I started to apply this in studies a few days ago. I sometimes I feel unconfident when I study like: it's impossible, it's very difficult,... . And I record my voice telling me good things like: I understood more difficult concepts like blah blah blah..., when I saw that difficult text related to X and I said: "Ohhh my god it's impossible to learn that" and finally I did it, ...

I think that it's the same apply that method in differents areas like: work or study.

I have to say that after to listen the audio I feel better but I think that I need more days to check if the method finally works.