Problem with ACER 5630-6803 video brightness

Hi,
I am not familiar with computers at all, so I thought I would come here, to where people seem to know what they are talking about to get an answer. I have an ACER 5630-6803 (T5500 Core2duo). I bought this computer last week, and when I viewed videos originally, everything was fine. Now, when I view videos from the internet ( Like on CNN or MSN Etc) they seem to be much darker then they were before. The same thing happens with the videos that came pre-loaded on media player. However, sometimes when I turn my computer on, the videos will be bright again. I have no idea why this is happening. I have not switched any "Brightness" levels on or off, down or up. Does anyone know why this might be happening? It happens when on battery power, and when plugged in. If this is posted in the wrong section on this website I apologize in advance. If anyone can help me with this before I take it into future shop to get it looked at, ( where it might be a simple fix, and I will look dunb) I would greatly appreciate it!
Thanks

 

Hi,

I recently got an Aspire 5634 (T5600, Core2 Duo) and find it also adjusts the brightness levels automatically. I think it may be adjusting itself according to what tasks you are performing but it does seem rather random at times.