where can i find transformer's driver?
Install Asus Sync. If you already have it installed, uninstall it, reboot and reinstall it.
i've read to try to install hydro JB or asus stock rom, but my PC now do not read the device (tf300t): so how can i install another rom if my tab can't load nothing via USB?
Try using different USB ports on your PC.
If you did it again, would it be re-tarted?
I was seeing the same thing in Austin, TX yesterday. The problem persisted in Warm and Miui, even after reprovisioning. I think it was a Sprint data problem. All is well today.