ok, so i just repaired permissions cause there was some strange things going on. (icons not appearing on desktop until finder restarted etc.) and now the imac wont sleep on its own, so i disconnected all bluetooth and usb, still nothing, also did a SMC reset, didnt help. thinking i may have to reset PRAM but not done it before, any one know how to do it on an imac 24"? also, should i wait until i get an external HD to back up before a PRAM or is there no risk from it?, cheers for the input in advance guys