Your best bet is not to identify what part it is, but what function it had and replace that function. You will have to unsolder the part anyway. After that, you can start working out if and how it is connected to the USB port. If it is, you know what it does and can replace it with something else.
It is possible USB might work after you unsolder the part. Perhaps it is just some peripheral part, not the power supply to USB. In this case, the fried part might just be shorting USB power, which then shuts down.
If not, maybe (danger!) you can connect the USB 5V directly with Mainboard 5V from, say the harddisk plug. This would change how safe USB is (usually it is limited to a certain amperage), and you could fry the notebook with USB. But then again it is already toasted...
This looks like a potentiometer with a built in on-off switch on the back.
When you either push on the knob or turn it to the end of it's range does the resistance between A and B change from infinite to 0 ohms? If so, you have confirmed that it is a switch.
The resistance between 1 and 3 should be fixed and between 1 & 2 (or between 2 & 3) vary as you turn the knob.
These are (were) commonly used as combined volume controls and on-off switches on radios before the digital age.
In response to the comment.
Since you measured an exponential change in resistance you have what is known as a logarithmic taper potentiometer. The other type is a linear taper. Logarithmic taper is used for volume controls since human hearing does not respond linearly but rather on a decibel scale.
If you measured across 1 & 2 instead of 2 & 3 you would have perhaps found the switch as "on" when the potentiometer is "on" as you put it. Looked at another way, the resistance across 1 & 2 will increases as the resistance across 2 & 3 decreases. In fact the resistance between 1 & 3 should remain constant as you turn the knob. Also for any place you put the knob, if you add up the resistance between 1 & 2 with the resistance between 2 & 3 that total should equal the resistance between 1 & 3.