Dell v715w printer constantly loses communication with computer.  We are using USB cable, not WiFi.  Have checked USB root hub power management and confirmed that the setting "Allow the computer to turn off this device to save power"  is NOT selected.  Am running current software and firmware. Followed directions on the Dell Support Center which indicated the anti-virus software might be blocking certain .dll files.  Have used three different anti-virus softwares - Norton, G-Data, and Avast - and on all three have tried shielding/preventing/omitting the folders containing the particular .dll files, with no improvement.  Have never had this problem previously with any other brand of printer.  Running Vista Home Premium 64 bit.  Please advise.