Scanner no longer recognised after an update

[Skipmeister]

I am running Wheezy 7.9 32 bit, with the kernel Linux 3.2.0-4-686-pae, and Gnome 3.4.2 on an Intel Pentium CPU G3420 @ 3.2 GHz. I installed a new printer in August, an HP Officejet 7612 all-in-one printer/scanner/copier, and it worked perfectly as both a printer and a scanner first time, despite not being listed on the supported list in SANE. Two weeks ago, I got a general software update notification, and did the update. Now the scanner is not recognised. The printer still works fine as a printer, but when using Simple-scan, I get the error message "No scanners detected. Please check your scanner is connected and powered on". I have had a look round on Google, and all the suggestions made do not work.
I tried the suggestion to add myself to the scanner users list on my PC which made no difference (even though the scanner previously worked without my being added to the scanner users list).
I have deleted the printer and re-installed it using CUPS, but that still has no effect. I tried re-installing HPLIP also to no avail, and I have now lost the toolbox on the drop down menu under <Applications> <Accessories> <HP Toolbox>, as when I click on it, nothing happens.
It would seem that something in the update has messed up Simple-scan. Looking at the dpkg log (is this the right thing to look at?) for the date of the update, I cannot find anything which directly involved SANE, so I think that it might be something else which has affected SANE. Has anyone any idea how I can find out which update did the damage? I don't normally do anything except accept recommended updates, so I am a bit lost as to what to do. I am not very adept at going into the system or root, so would need something pretty explicit to follow to try to find out the cause.
Many thanks.

[bigrigdriver]

Use your preferred package management tool to see if package libsane-hpaio is still installed. The problematic update may have removed that package, but it is needed for imaging functions of the Simple-scan.

[Skipmeister]

Hi,

Thanks for the post - I have had a look, and I have libsane-hpaio 3.12.6-3.1+deb7u1 installed. The package manager suggests that users of hplip have hplip-gui installed as well, which I have already got installed. Any further thoughts? I guess that this may be a long slow road...

Thanks