depending on your model# laptop, there are replacement parts. The costs do come in for your decision. We have no clue, but Google for your laptop model# and see if parts are available. Even an old laptop can be fixed this way. You could even buy another old (same)model laptop from online sources, like Craigslist or Ebay, etc..
Alas, windoze isn't geared to run from ext. USB drives. There maybe some form of USB windoze that are mobile but these tend to be so limited or outright expensive and may not be supported if your laptop is that old. I practically think these are dead-end setups. As you have it, it just won't work as if nothing happened, probably just a blank display.
http://windowsitpro.com/windows/run-windows-any-usb-flash-drive
tada -----Willy 