if it's just started maybe it's the disk brand ?......i had this problem infact i have it now and i solved it by removing it from the ide cable, it rebuilt my pc and put it in the middle of the ide cable, ( don;t know id your mates been messing about ) so i simply moved it ot the end......now i don't know if that how my set up is at the moment i can't be arsed to open the bey'atch back up.......hope it is a lens cleaner that be mighty fine !
good luck.