Device not recognized?

Hi,
I hooked up a L293DNE to the arduino and a motor to the h-bridge. The first few times it worked fine, but then suddenly when the motor changed directions it spined for a bit and then stopped. My computer showed that the device cannot be recognized. And since then i cannot see com port of the arduino in my devices.I have also tried whit other computers, but theres no response. But the arduino seems to be working fine. Even if i plug it via usb. I cannot tell if the sketch works because it needs to be triggerd via serial. What could be the problem?
Thanks

What could be the problem?

Simple the USB to serial chip has stopped working. If this is a death of natural causes or if you hastened it's demise it is hard to say with the information you posted. As you don't say what sort of arduino you have I can't even tell you what chip you have for this function. Were you using the 3v3 output?

Thank you for a quick response. I am using Arduino Uno. And I was powering the bridge and the motor whit 5 v output. The motor draws 0.36 mA from my calculations. So this shouldn't be a problem.

The motor draws 0.36 mA from my calculations.

I would do your sums again that is way too low. Were you driving the motor direct from the arduino pin? If so you can't do that.

I used the 5V output pin on the arduino which was connected to the breadboard and then into the Vs(unregulated voltage) pin on the bridge.

It is possible that the crystal into the USB chip has failed, can you check this with an oscilloscope? Otherwise it looks like the chip is dead, sorry. From you description you have not done anything wrong but you might have done something that you don't realise.

Well this sucks. Just to be sure I will try replacing the USB cable but it probably wont do anything.
Thank you for your help and time.
EDIT:
I orderd a rn41 bluetooth module and i was wondering if i could use it to upload sketches to the arduino?

I don't know you can start researching it here:-
http://www.arduino.cc/playground/Learning/Tutorial01