the last few days I have had a problem with my iMac. I have the wireless mouse and keyboard. First the mouse stops registering the scroll ball and mouse click, however the pointer still moves for a while and then that stops to! At this point the keyboard stops responding too. I tried to put the mac to sleep by pressing the button at the back once but nothing happened. I had to hold the power button and restart. After the restart it is all ok! This has happened about 3 times in as many days! Can anyone help out as I'm fairly new with macs and don't know where to start?