USB Over Current Notice

Is this error caused by your external HDD? The keyboard, mouse (assuming that it's the Apple mouse that came with your iMac) and printer shouldn't cause any problems. Disconnect the HDD and see if the problem goes away.

If the HDD is the problem, is it a powered drive (with it's own AC power supply), or a USB-powered drive (without an AC power supply)?
If it's USB-powered, the USB port on the iMac probably can't supply enough power. Buy a powered USB hub (hub with an AC adaptor) and connect it between the iMac and the HDD.

The attached device causing the problem needs to be plugged directly into the USB port of the computer, not into your keyboard.

On a second reading of your post, go with clockwork's advice, as mine is not relevant.

Hi, I have a new iMac 20" and yesterday I started to get the same warning, and now it comes up each time I log in. But, I do not have anything plugged into a USB port except the Mac keyboard (and the mouse is plugged into the keyboard). This is the way I've had it since buying about a month or so ago.

At the time it started I was running a number of memory hungry apps, such that 2Gb of RAM wasn't enough to stop it slowing (in case this is relevant).

Any advice?

I have the same problem... I've got five new Intel iMacs in a lab. They are each starting to present me with the "USB Over Current Notice." The only thing connected to them currently are their keyboards. I did have a USB driven musical keyboard attached, but even after removing them, I still get the notice. What should I do?

Hi, my advice ->
Reset SMC - Repair Permissions - ReBoot individually after BOTH tasks.
http://support.apple.com/kb/HT1543
http://support.apple.com/kb/HT1452