I'm having some USB power problems with my iMac 20" (late 2006) So to start, my iMac has 3x USB 2.0 ports of which: 1 has my 3.5" eternal HDD plugged in (it has its own power) 1 has an extension plugged in so that I can plug in flash drives 1 has a 4 port USB Hub plugged in. It doesn't have its own power source. plugged into this is: a printer (off most of the time) iPod shuffle dock iPod dock Keyboard (mouse plugged into keyboard) I havent experienced problems in the past. I can plug in two iPods into both the docks and not experience problems but the problem comes in when I plugged a 2.5" external HDD into the USB extension. The problem was that I couldn't use the mouse. I had full keyboard control and the mouses' optical light was still on. It was just unresponsive on screen. Is my USB setup underpowered? or is there some other problem? Also; is USB power given per port or does the entire system have a limit?