20" Cinema Display Resolution Problems???

Hello friends,

I have a 20" Cinema Display that I'm using with my Macbook Pro from 2008 (2,4 GHz, Intel Core 2 Duo, 2 GB RAM), running OS X 10.6.8. The resolution on my Cinema Display was perfectly fine, with crisp images and sharp text, up until about a month ago, when it started to always look "just a little blurry". I did not change any settings, display preferences, have already tried resetting PRAM, but nothing works. All the cables are fine, intact, no damange. The strangest thing is that it can be sharp on the Cinema display - when I click on "turn on mirroring", then it is sharp (but obviously then I can't see my documents on the screen because I only see them on my Macbook Pro). Do you know what I mean?

I can't seem to find any solution. Help??

Thanks to all in advance!