Hi all,
I've done some searching online but I haven't found a direct match to my problem. When I was working with my Arduino yesterday, I plugged it in and tried to install a program. It worked fine. A couple of minutes later, I got a Windows notification saying that the USB device I plugged in was not recognized. Since then, my Arduino has not been able to connect to any computers. I tried my laptop as well as a Mac desktop. It receives power, the lights on the board all turn on and the Power pins are working, but it just isn't recognized by any computers anymore. I tried reinstalling the Arduino software and drivers, but that didn't work. I've also switched cables. Please help.
Sounds like you did something bad to it.
What kind of Arduino is it?
Was it connected to any external devices? If so what?
It's an Uno. It was connected to an Adafruit Motor controller when it conked out.
Were you supplying SEPARATE power to the shield and if so did you have the power bypass jumper on or off ?
Always supply seperate power to motor shields and make sure the jumper or trace is set to the correct position.
Power problems with motor drivers seem to be a very common cause of damage to the 16u2 on boards that have that serial adapter.
The shield did have separate power. The jumper was not on and the power LED was green so the shield was getting good power, though sometimes the motor shield had to be gently pressed onto the Arduino's pins to get a good connection. Maybe i pushed too hard or something?
double and triple check all the pins are in the correct headers and that NOTHING can short against the bottom of the shield.
Some shields come very close to the USB connector and in those cases sometimes a strip of insulating material / tape can be useful.
Ethernet shields are especially prone to that issue.
It doesn't work even with the shield off. I took everything out and it still won't connect to the computer. I think I'll just have to buy a new one.
Yeah 
You can buy el-cheapo clones on ebay for like a tenner (these have CH340G instead of 16u2 most of the time, meaning you have to dl and install the CH340G drivers. Anecdotal evidence suggests the CH340G is more resilient: I almost never see reports from people here who've trashed their CH340G on their arduino clone, but 2-3 people a week post about trashing the 16u2 on official boards like you have - usually with a motor driver shield too) - this is probably what I'd use. I use clones exclusively, personally - periodically I donate some $ to Arduino to make up for it.
Thanks for the help, guys, I think I'll just buy a new one and be more careful with it.