I had a similar problem when I upgraded my Toshiba Satellite A300 from Vista to Win 7.
Now fixed - read on!
I uninstalled the device and then reinstalled and win 7 says was is successfully installed. Then I rebooted, just in case that made a difference.
But it still doesn't work.
Today I searched further on the web. Several blogs had people reporting a similar problem and the answers suggested it is a registry problem, although the way to fix it looked a bit too techo for me to tackle!
I searched the Toshiba sites (which are a minefield) and eventually found a page that has a list of items to reload after upgrading to win 7 - specifically for the A300 32 bit.
I noticed there was a registry patch for printers and devices. Aha.
Downloaded it and ran the .exe.
Rebooted. Presto - it works!
The link is www.isd.toshiba.com.au/support
Enter exact details of your computer in the boxes on the right hand side.
To the left of the boxes just entered there is written in red "for windows 7 drivers click here"
On the left hand side again you need to select your computer model - Satellite A300.
Then you finally get the list. Download and run the patch for printers and devices.
The rather funny thing is that they are not all drivers - however, lets not be too picky - at least it fixed my problem :-)