Hp nx9000 USB

Could it because the power support of USB? If I buy a USB hub with power support, do you think it will be better??

You may have hit it on the nail. I had a problem one time with a usb external floppy drive, just wasn't enought juice coming from the laptop. I got myself a powered usb hub and everything's fine now.

http://bizsupport1.austin.hp.com/bizsupport/TechSupport/Document.jsp?lang=en&cc=us&taskId=110&prodSeriesId=324375&prodTypeId=321957&prodSeriesId=324375&objectID=c00035553

If the device displays as an unknown device, check the following items:

  2.
     The device may not be getting enough power. If other USB devices are connected to the system, remove all other USB devices (except keyboard and mouse) and restart the computer. Check Device Manager again. If this solves the issue, use a powered USB hub to power more devices.

http://bizsupport1.austin.hp.com/bizsupport/TechSupport/Document.jsp?lang=en&cc=us&taskId=110&prodSeriesId=324375&prodTypeId=321957&prodSeriesId=324375&objectID=c00820529