Are you using Windows Live OneCare? If so, I have never heard of OneCare blocking an external drive from functioning. I assume that you mean you've been in contact with the drive manufacturer's tech support. If you wish to confirm that their suggestion was false (or true) and you are using OneCare, open OneCare, click n Change Settings, and disable the firewall and the virus protection on the respective tabs in the OneCare settings. If the drive works consistently then, I'm wrong, but I believe you will find that it does not make a difference.
-steve