Jaap,

I do hope your conclusion is wrong, but the signs point the direction.... I agree.
You checked the PC-USB with another USB device didn't you ? (Just to eliminate the possibily of a defective USB-port)

How could a defective Tyros-USB port lockup the PC ? Shorted power-cicuit ?

Are you telling the MIDI-out of the Tyros does not work anymore since the 'accident' ?
If this is true the problem might be bigger then your USB port.

I hope it is easy to solve and Yamaha is able to solve the HF-sensivity of the USB-port.

groetjes,

Roel