Could possibly be broken down or faulty scanner.
read this page and go over the steps.http://h10025.www1.hp.com/ewfrf/wc/document?docname=bps05270&lc=en&dlc=en&cc=us&lang=en&rule=23276&product=77368
Also try to completely uninstall the machine from your system, first by uninstalling the software, start -> control panel -> uninstall programs or "add or remove programs". find the scanner shoftware and related and uninstall them.
then open the device manager by right clicking on my computer you should find it from your desktop or from the start menu, right click and select Manage.
on the management window on the left side select device manager, now on the right side, find imaging devices, right click on your scanner and select uninstall, if you have the option also check uninstall driver software.
make sure there is no trace of the scanner in device manager and then unplug the scanner.
Restart the computer.
now with the device uninstall and the programs uninstalled. download the latest software for it fromhttp://h10025.www1.hp.com/ewfrf/wc/softwareCategory?lc=en&dlc=en&cc=us&lang=en&product=77368&
install the softwares and plug in the scanner when asked or after the setup.
the scanner should get installed in few minutes after which you should be able to scan, if not then restart the computer.
Try scanning anything and see if the problem is still there or not?