Hello again.
Thanks to your help, I managed to install 10.8.3 in my 4540s a few months ago, using probook installer 6,1.
Since then, I have been experiencing an annoying issue: everything works fine, but, randomly, the laptop shuts off (and automatically restarts) without any apparent cause. I have tried to monitor temperature, but nothing relevant happens. I can´t find the reason, and looking in the forums, I can´t find anybody experiencing the same problem. It happens in any situation, whether I´m just using an internet browser, copying a file, or doing heavy tasks like sound mixing or 3d composition. It seems like there´s no pattern in this behaviour. It just shuts down, and after 3 or 4 seconds, restarts, then, the first thing I find is a white screen with a message about a Bios warning (something about "Cmos"?), I have to press enter and then it restarts normally. Some days this doesn´t happen at all, other days it happens 6 or 8 times.
Any ideas??
Thanks for your help