Power to USB, thunderbolt ports, but no signal or data transfer

There is power flowing through the USB Ports. I tested that with a USB tester and am getting the standard 5v of power.

When I connect a variety of mice or keyboards or other USB device I can get response on the actual devices (i.e.: mouse lights up, keyboard power LEDs illuminate). There is no reaction or response from the computer. The iMac starts up just fine, but the mouse pointer stays in the top left corner and will not move. No keyboard response.

I can't do any kind of test (i.e.: AHD) or enter single user or target mode without the keyboard.

There is nothing in the optical drive.

I would normally do a system profile check to find the missing components, but since I can't choose an account or type the passwords, I can't get past the log on screen. That's as far as it gets.

I have tried:

• a variety of USB keyboards and mice

• removing the harddrive to see if it would read to:

— an external hd with Mac OS

— an external cd drive with a Mac System Disc

— a bootable USB flash drive with Mavericks install

• target mode

• external monitor via thunderbolt

• connecting another mac via thunderbolt

Still nothing.

Please help.