How can a usb device crash a computer?

[joe at actionline.com]

How could plugging in a printer via a usb port crash my computer?

I just got a usb to rs232 connector cable and when I plugged it
in to my computer, the computer instantly quit. So I unplugged
the usb cable immediately, but now I cannot power on the computer.

What in the world could have caused such a drastic failure?

And what can I try to resurrect the computer?

Or, to whom would you recommend I take the computer for repair?