Communication problem Arduino / PC

Hello,
Since yesterday, my computer does not recognize Arduino, I installed 2 times the Arduino software and reinstalled drivers, also tried with two different arduino without getting results,

I'm using Win 8.1 and I'm doing a project using Labview

Thanks

Genuine or clone?

And maybe an English translation of the error...

The error message is 'device driver for device could not be loaded'.

Problem is in the driver. Why couldn't be loaded? Check the error in the system events. Code 39 means: Windows cannot load the device driver for this hardware. The driver may be corrupted or missing or there is registry issue. Try to reinstall driver via device manager. The driver is included in the Arduino SW. COM6 is little bit higher number. Are there any unused ports? Remove them if so.

Indeed try to delete the Arduino in device manager and be sure to select remove driver. After that, replug the Arduino into the PC and point the driver installer to the Arduino driver folder.

Same problem here
Windows cant find driver and arduino port option is grayed.
Can`t find way to install driver.
are you also using windows 10?

This is shown by the device manager

If your Mega 2560 really uses an Atmel chip as a USB-to-UARt bridge (such as the 8u2, 16u2, 16u4, etc) you can try reflashing it with its firmware.

It has its own ICSP header exposed, and you need either another arduino (using the Arduino as ISP sketch) or a ISP propgrammer to reprogram the 16u2.