imac screen goes black at 50% brightness
Hi everyone
This is my first post in this community - I would be so grateful for your help. In late 2011 I bought my wife the biggest screen imac - it was a mid or late 2011 intel version. Since then for one reason or another she has hardly used it - perhaps it has been switched on for a total of 3-4 months over all that time. Anyway, I have kept the operating system completely updated and we've started using it again recently - but something strange has started to happen. When you adjust the brightness to 50% or below, the screen goes completely dark. And when you have it on 100% brightness, it's not that bright - probably about where 50% used to be before! Now, it was brand new and hasn't been used much, so I cannot believe something could have happened to the bulbs. It seems like the brightness control is somehow out of sync so it thinks 50% is 0% and 100% is 50%!! I have googled around but cannot find anyone who has had this problem - unless I'm using the wrong search terms. Can anyone please help me out? It's so frustrating!
Many thanks in advance
James
iMac, OS X Mountain Lion (10.8.5), intel