try different USB ports...dell uses cheap motherboards and not all of the usb ports (if any) provide the Voltage that they should...there is a fix however...you can get a POWERED usb hub for around 10 bux online, or 20 in a store...thats probably the problem...though dell has gotten better, this is something that they still do (mine at work, the front usb port is powered, the 3 on the back are not..)