leonardo stop being recognised from windows 8

i was a happy arduino leonardo user for 2 days. Everything was ok, after downloaded and installed the latest up to date adruino IDE i was able to run a few tutorials. Every time i upload to leonardo my code, the computer sounded like disconnected and reconnect the leonardo, so that the code was send from my compouter to the board. Every now and when i had to reselect the com port on the IDE. For no pparent reason, in my last attempt to upload some code to leonardo, an erron message appeared that the com port was already in use. From that moment on i have tried numerous things, from arduino forum to the internet, but my computer cannot recognise leonardo. In the device manager, at Ports, Leonardo is always with a yellow exclamation mark at COM7. Sometimes when i reconnect the arduino, the exclamation mark disappears, things appears to be good, reselect the correct port on the IDE, but when i run my code the same error appears "com X port was already in use". I have also noticed when i press the reset button, in device manager, arduino appears as "arduino leonardo bootloader" on a different port, stays like that for a few seconds, and i end up with Leonardo on some port with the exclamation mark.. any ideas please? ouffff

(deleted)

hi! i can not make my computer to see my arduino - keeps disconnecting...so i am not able to upload any code..

I have same problem. I was able to go to the Intel driver set and reinstall usb serial devices (com port). I'm using Arduino Nano and found I am now able to verify, compile and uplaod programs onto board. The minute I attach the Vcc (5v or 3.3v) and ground pins the com port drops out again. Disconnect pins and the port shows up again on device manager. Trying to complile with pins connected gives a aduino error message