If you are using USB port to connect Benq scanner, please forget about the on board USB port (USB support from VIA or Nvidia chipset is faulty). Probably you will need to buy a USB 2.0 daughter board (NEC chip set is more compatable). Since you bought the scanner last Aug, it is impossible to ask the original seller to replace it. So. this will be the best thing I could suggest.

If a new USB 2.0 card doesn't work with Benq, you probably need to buy a new scanner. Well, go for those name brand products (e.g. HP. Agfa ... little expensive, or Umax, Microtech .... almost perfect .....Mustek is less reliable .... as to the rest product I have no comment). I had bad experience with Benq scanner too, finally it was replaced with a Microtech.

Good luck