Fernando
I suggest to find a good guide to collimation on the internet, print it out and go through step by step. There are plenty of good ones available, for example:
LINK
Don't assume anything and don't skip any steps. A bit of practice and it will work out.
On top of that, I think I have the same scope as you - so I might have some helpful advice.
I noticed from robofocus numbers that when the scope is moved from horizontal to vertical, the mirror rocks back into the cell, sometimes this takes over 1 hour to complete. So if you collimate with the scope on a bench (horizontal) and then do a star test (vertical) you will get some movement that can throw it out of focus and collimation. The solution in my case was to attach the mirror to the cell with silicone instead of the sticky pads, put some silicone inside the ball joints in the primary mirror cell and add some tensioning bolts to the cell. In the end I think it was the ball joint caused the issue.
James
Edit:
Here's another one:
http://www.cloudynights.com/ubbthrea...Number=5053116