Sorry you're have difficulties with your scanner. HP usually just works, printers and scanners. I do see you are posting in the KDE4 Support section. I still use KDE3.5, so my experience may not apply to you.
Maybe someone more knowledgeable can jump in and help because I'm just shooting in the dark, but... in the mean time...
Do you have SANE - local and remote scanner access, and Graphical frontend to SANE as well as xsane installed. You might uninstall and re-install them to see if that changes anything. That's done in synaptic
You might post your computer specs, the contents of /etc/sane.d/hp"your scanner #".conf. I currently have three different ones, plus an hp.conf in that directory.
Also, you might list the hplip.conf in your home/user/.hplip directory. My hplip.conf in the scanner section is:
scan=/usr/bin/xsane -V %SANE_URI%
Keep pluggin' away,