Brightness Problems

So I don't really know anything about the computers, but I've noticed that whenever I unplug my charger my brightness dims down to a point where I know its on, but I can't use it. Usually I have to put my computer to sleep and turn it back on to get it to fix. Also, the brightness wont adjust in anyway when its on. I've tried the function keys and the setting in the side bar. I have a toshiba laptop running windows 8.1 if that helps. I also have recently completely wiped it thinking it was a virus of some sorta with no change.

mco2166, sorry so late for a reply. If you haven't already fixed it then I'm going to assume you have Intel graphics, so go to Device Manager and disable the Intel display adapter, then re-enable it. See if that helps with not being able to adjust the brightness.

As far as it going so dim when you unplug power, that is probably your setting in Power Options.