Hi again people, Just recently my mac screen has been breaking up into horizontal pixilated strips about 20mmx 2mm giving a blocky appearance ie one block of strips is off by a strip on the next block and so on over the whole screen. The other thing is the revolving rainbow comes up on the screen as if the mac is doing something. The only way to clear this is to physicaly shut down the computer and restart as all the system locks up. Is it something the mac has caught or is it a sign that my mac is in need of some workshop time? Thanks all iMac Power PC g5 , OSX 10.4.11 running Firefox.