I've had similar issues wth printer/scanner drivers.
If the driver didn't come with an uninstaller the easiest path may be performing a search for HP ModelNameHere and deleting associated files. Alternatively, you can open System Preferences, open the Users section, select your account, open the Login Items tab and unselect any related items. Restart and driver won't load on startup (if that is its current behavior). Obviously these solutions may hinder your ability to use the printer.
In any case, it would be worthwhile to disable the driver and see if it is in fact the cause of the sleep problem.