Hi there maillet,
Your USB stick shouldn't disconnect.
Have you tried other USB sticks/drives? In case you haven't, it may be a good idea to do so.
Have you tried attaching the flash drive to the ports on the back of the computer case? These ports are directly attached to the MOBO.
Another thing you can do is to just go to the MOBO's website and update all the USB drivers.
If you attach the USB stick to another system, you will be sure whether there is something wrong with your system or with the drive itself.
Cheers,
D_Know_WD