Hi Stuart,
Welcome to the HP Forum.
The Full Feature Software for Windows 8.1 is now under a new umbrella program called the Printer Assistant. The package is installed as one would have installed the Solution Center in the past.
HP Photosmart Full Feature Software and Drivers
Once the the driver is installed, you may see an icon on your Desktop for the printing program else take a look in the printing program's folder for an executable (C:\Program Files\HP\<printer name>).
Example extension "Printer Assistant" for the Photosmart 7520 printer program:
C:\Program Files\HP\HP Photosmart 7520 series\Bin\HP Photosmart 7520 series.exe
The Printer Assistant provides much of the same functionality of the Solution Center including a feature (when available) called EWS (Embedded Web Server) management.
See your printer's User Guide for more information.
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HP will never call you on the phone and ask for money to 'keep your PC safe'.
Say “No, thank you,” and hang up!
Cybercriminals might call you on the telephone and claim to be from Microsoft.
See: Microsoft Safety & Security Center
Mark my answer “Accept as Solution” when it provides a solution or workaround!
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Click the KudosThumbs-Up!
It is a nice way to say “Thank You" for the help.
Although I strive to reflect HP's best practices, I do not work for HP.