An HP PSC 2410 photosmart all-in-one printer (thats the printer fax scanner copier model) won't print anything. When its first turned on you can hear a constant clicking sound. If you look closely at the scan head its lit up and moving slightly, almost like its jammed.
The problem was caused by dirty glass and the scan sensor not responding correctly. Dismantling the top of the scanner to clean it is straightforward - once you know the magical HP sequence to dismantle the top and take the 5 screws out.
You'll need a Torx T-10 screwdriver and to take a look at the photos in this HP document
Basically, unclip the scanner cover, undo the 3 screws, prise the control panel cover off from the front edge. Gently push the catch into the hole below the Black copy button. Slide the panel towards the front. You'll find 2 more screws under there that will release the glass. Clean the underside and re-assemble.