somebody must have enabled the bios password in your computer it cannot happen automatically this is a security feature to prevent theft and use.
Just press enter without entering any password if it is not accepting then you need to contact the service centre to get a new password which they willl generate after verifying the ownership. It should not be costing you anything.
In this case you need to upgrade the bios firmware using another computer, you need to click the link below once you open the acer page select the correct model number and then dowload the flash bios update driver which will by pass the password after the upgrade. you need a flash drive to transport the file to this computer follow the instructions it will create a bootable drive to the flash drive once you boot this computer with the flash drive the problem will be solved.
http://gd.panam.acer.com/home/
Computer Hardware Engineer
Bachelors Degree in Science (B.Sc.) Over 11 years of experience in Technical Support