Are you working on batteries or power.
Did you install the graphics drivers from the acer cd.
Waiting for your response.
If your function keys do not work to the best place to go power management. Set the computer so as to achieve maximum performance, and should increase the brightness of the screen. If this also does not satisfy then you can do this, you can increase the brightness of the screen at any time in the BIOS.
There are no other ways beyond these.
Either you need to reinstall the graphics driver from the disk or try to go into the BIOS and look for brightness control. If both are not feasible then there are no other ways to have the brightness controlled.
Please let me know if this information helps.
As I am running out of ideas at this point of time I would like to opt out of the question, thus allowing other experts to assist you.