A lot of people have had issues with the USB logger. Best solution is to call Davis and exchange for a serial version.
Some people have found that Windows turns off the USB device after awhile to save power. You can edit that device in the driver section and see if the advanced properties have the option to turn off power saving features for that device.
Others have found a different USB driver that helps. But if those don't, Serial is your best bet.
I went out of my way to buy a new PC that still has the serial built into the mother board. Of course, when I bought a VP1, serial was my only option. I've decided to keep it that way. BTW, the Dell Vostro 220 mini tower has serial still...