Hi Ballo, thanks a lot for the answer.
Today I uninstalled my SL viewer again, then I uninstalled the Video Card drivers.
I downloaded both, the last SL viewer and the beta one.
Using REVO I deleted all the drivers and the old NVIDIA ones from my old graphic card.
After all these, I downloaded and installed the latest Microsoft Net 4.0 driver.
I reebooted and then I installed again the ATI Drivers and the CATALIST software.
Reeboted and then installed the SL VIEWER but everytime I wanted to use it, a 00000014 (more less) error appeared and then It crashed. I found using Google that I should rename the winmm.dll file in order to start ok but in my case I just could watched the first screen, then it crashed again.
So then I installed the Beta Viewer, I renamed its winmm.dll and good news. The last beta version worked without any problem until now, so I am using it to get into SL.
By the way, in the next message I will post my full log file as you asked me to do.