Yes, of course. It was my first choice. Later, I tried the escape key. In both cases, no results. I've tried too the F12 key to enter directly in the boot sequence, even knowing that if the BIOS didn't let me enter in the main settings, surely neither in the boot sequence. In this case, simply ignored the key. I supose this option is disabled.

And yes, I'm perfectly aware that "absolutely sure" can seem a subterfuge for no accepting I've lost or forgotten the password. But this is not the case. I know that creating a BIOS password is playing with fire and I've always avoided it. I use to test different OS in my computer with USB pendrives, and use to test recovery tools this way, too, so the last thing I'd like to do is putting myself in trouble. Besides, the Aspire is my home computer and the other only person at home is a six months child, so I don't need any password (and the child can not even walk yet, less change BIOS settings...).

Thank you for your answer and forgive my bad english. I'm catalan and english is my third language. I hope it to be understandable, at least.

PS: If it can help, before the upgrading the first item in the boot sequence was the USB option. Now is the harddisk. CD's don't work either, so.

That's the usual solution I've found in the Internet, but scaries me to the death, because I'm no a hardware wizard at all. Besides, I had to fight a complete week finding the right UEFI settings for a usable dual boot system (Win8 and Linux Mint): disable secure boot, etc. It was a nightmare. Well, it seems I'll have to try it, of course after a backup. All this setings will be lost, too? Or only the password?

Incidentally, after getting all right, Win8 erased twice my MBR (even without Internet connection!!), letting me without accessing Linux, and I had to restore it USB way. That's another reason to need changing the boot sequence.

Thank you very much for your fast responses. Even more, on Sunday :-)

A very good suggestion, but I only need to switch to Windows a day per month, for running only one program without Linux alternative, because my job. I run Linux since the '80s (Slackware with 16 floppies to install, a lot ok kernel compiling ;-) ) and suits perfectly my needs without need of any Windows program until now, so running it as a virtual OS under Windows has little sense. It would be like going back to the Stone Age again. I'll try your CMOS solution and try to redo the right BIOS settings, crossing my fingers.

Thank you!