You need to take the ND-100 outside with a clear view of the sky. Moreover, use the provided USB extension cable to extend the receiver away from the host device.
One quick question, what is the status of the LED? Is it off, steady on, or is it blinking?
Open up the MiniCDU program. Select the designated com port and proper baud rate. Press Connect. Check the Fix section to see if you're still getting the 'Invalid' results.
You can also perform the Cold Start process. Under the TTFF Test section, choose the Cold Start option (if it's not selected) and press Start. Wait for a few minutes and observe the Fix section.
As for the firmware update, just keep disconnecting and plugging in the ND-100 until you manage to update the firmware. By the way, where did you download the firmware update from?
Let me know how it goes.