florin_radu94, well, maybe you have some background apps running that do sth with calls, like a call recorder? Probably thats why its getting so slow... and also on my old 6120c I also had similar problem, but it didnt bother me a lot well, if the battery is low its pretty logical that phone reduces display brightness, but in your case it seems like something is seriusly wrong. Is only the background light turned off or also the screen itself?