I also once owned an Medion MD 90012 with the same problems.
Pressing F11 -> Password required.
I spoke to the Person at Medion who knows this password about 1h. He didn't tell it to me. He is afraid that this Pass will get public by internet-forums, and so people that don't know much about pc's will make some changes so that the machine don't work properly and they return it in waranty-time to medion. So Medion will have a lot of work more.
As he said there are just 2 people at medion who knows this password.
In my case there was an option to disable "only boot from Medion-CD" that i wanted to disable, so i can install Linux on it. --->
No Password, No boot from other CD's, NO MORE MEDION !!!
