How can i restore my screen brightness in Windows Vista?

I have Windows Vista Home Premium. The problem is this: either my sister or my niece changed the screen brightness via Windows Mobility Center. I tried to change it, but the screen brightness slider goes only to 70. I can't put it higher than 70 because the slider is all the way at the end. HELP!!!!How can i restore my screen brightness in Windows Vista?
Go to control panel then power options to the left it has 'adjust display brightness%26quot;