I have a nikon coolscan
Hi, well if you have used Vuescan a "driverless" program, then unfortunately the unit may have a damaged interface? As this software will/should work without any drivers being installed, as it works as we say "Natively".
However in saying this please ensure you have the latest drivers installed, download from the manufacturers website to be sure.
You did not indicate what operating system you were using, if using Win 7 64 bit, or any 64 bit OS, ensure that the drivers again are installed correctly, installed and setup as Administrator, and you may have to set to OFF, the Driver Signature Check at boot up, to set & check, press F8, at boot up, and select from the bottom of the list, this will ensure that the driver is definitely loaded at boot time.
Always try, install and use, any suspect equipment on another PC, this will "Prove" where the fault lays.
Adapters can always a problem, if possible try WITHOUT any adapters at all. ie: Try on, another or even perhaps, a friends PC that has a Firewire port built in just to prove if the device is actually functioning.