Printing Errors or Lights & Stuck Print Jobs

My 7640 no longer will scan.   For some time, it would not "scan to computer" from the printer, but I could initiate the scan on the computer and it would work.  It still says, "The connection to the computer has been lost" when scanning from the printer (i.e. it still doesn't work), but now it won't scan from the computer either.   I ran the HP Print and Scan Doctor and it scans a document and the printer says it was successful, but the Scan Doctor says, "The HP ENVY 7640 was not found."  Obviously it found it, but there is some problem.  It hangs displaying the "Finding and fixing scanning problems" window with the smaller "Scanning ..." window, but doesn't resolve the problem.

I have uninstalled the printer and then reinstalled it using the driver downloaded from the HP site, but it won't work.  It prints ok, but it won't scan.