Okay...
Which OS (and sp if appliable) are you using? (Win7? Vista? XP? other?)
And who made the usb dongle? Is there a model number?
For me (Win7 - Home - 64 bit - SP1)
Disabled is more grey than black and white...
and there are some color components when enabled.
Do you have administrator privileges?
And when you "right click" on the dongle after trying to enable it...
does it offer the option still to "enable" or does the option now say "disable"?
After enabling... you might try rebooting,
though I would think that should not usually be needed.
If all else fails...
make sure you have the CORRECT drivers on a drive / thumb or cd,
then go to hardware manager
and try updating the drivers by pointing to the source you want to use.
Finally, if still no joy, you might go to device manager
and get "harware ids" and "compatible ids", (for YOUR device, obviously).
This will be under (right click) properties -> (tab) details,
the second and third menu items (if your OS is the same as mine.)
And we can work to make sure you do have the right drivers.
This SHOULD not be this difficult! If I can't get you there, I know a couple of guys to ask though.