I can't switch from Blender render to Cycles render I'm having problems by switching rendering. The problem is that Cycles render doesn't appear in the top. There's only Blender Render and Blender Game.

Also when I run the program, a windows opens up in the user preferences and everything that was before is gone. I don't know if I did something to my PC or Blender files.
make sure that cycles is enabled in your add-on panel in your user preferences. also it might help if you upload your blend file with this problem.