I see this happen all too often.
A customer brings me a laptop, and a USB internet modem (the usual 3G SIM card device).
She says it was working perfectly on her old PC, but refuses to work on the new laptop.
She spends many hours on the phone to Telstra/Bigpond technical support, only to be told that the fault must be with her laptop (which is just a lame Bigpond cop-out, since the laptop is brand new).
So she brings it to me, and I try it on a different PC, and it does the usual thing:
Initially connects as a virtual CD, then automatically installs all the needed drivers, then sends a special command to the USB device to flick it from a virtual CD drive to a USB modem, then everything works as expected.
But on the laptop in question, The USB modem is already working in modem mode, but doesn’t have all the drivers it need to operate.
This can happen due to a customer cancelling the driver installation before it complete, but it can also happen if the driver installation software encounters an unexpected problem (usually due to new hardware/software, or due to software line antiviruses that interfere with the installation).
Anyway, for me, the solution is quite simple:
I connect the laptop to both the USB modem, and also to my local internet connection via ethernet.
I can then update the missing drivers over the ethernet internet connection.
Once the drivers are updated, I can disconnect the ethernet, restart the PC, and the USB modem connects normally.