Sounds like the kernel panic message ("You need to restart your computer. Hold down the Power button for several seconds or press the Restart button.", see attached image).

Usually it's a software issue, although it could be hardware.

What version of OS X are you running?

Do USB devices cause kernel panics if you boot into Safe Mode (hold the Shift key when the Mac starts)?

First, I would reinstall OSX, do not plug in any devices and do a backup on a DVD, clean install OSX and see if that helps

That device may also be bad, try a different USB device in that USB

Try it in a different USB port, that USB may be bad and if you want to use it in this case, you need a logicboard, otherwise a USB hub will be fine in a working port