Arduino Uno overheating

So I am working on a project and have proceeded to overheat two Uno's in less then a week. We figured out what was going on. My question: Is there a way to fix the Uno's? When I plug them into a USB cable, the light comes on, but the computer does not see the device on the Serial Port. Any suggestions would be greatly appreciated.

Thanks!

If you pull the 328 out, does the problem still occur? That is, is the 328 interfering with USB?
If the USB/Serial chip is dead, you're kinda outta luck - need hot air rework capability to remove/replace the USB/Serial chip.
What are you using for a power source?
What are you connecting up?

Overheating how?

Killing the atmega via supplying > 5v or drawing too much current?

The fact the usb port does not show would imply you fried it, but the work it takes (unless you have a heat gun) to replace it... you could buy a cheap usb to ttl and try programming it via tr/rcv pins 0/1 simple as that bypassing the onboarf usb ic