This solution was posted for a similar problem with a PSR800 unsigned driver and Windows 8:
Windows 8 installation of unsigned driver for GRE PSR800
1-Copy .inf file from the PSR800 CD to a folder on your computer
2-When you are signed in to Windows 8 as Administrator connect the PSR 800. It will then attempt to load the driver and appear to succeed but the driver will not be working at that point.
3-Load the Charms Bar by pointing the mouse at the upper right hand corner of the screen.
4-Select Power and hit restart while holding down the Shift key.
5-A selection of Troubleshooting options will come up, select the Troubleshoot option
6-Another page will appear, select Advanced Options.
7-The next page will display several repair options, Select the Startup Settings to change the behavior of Windows Startup and then click restart on the next page.
8- A menu with 9 selections will appear. Select #7 or F7 to disable Driver Signature enforcement.
9 Windows 8 will restart.
10-With the PSR 800 still connected open Device Manager from the Control Panel. Select the Com port assigned to the PSR 800 and select Update Driver.
11-Select Browse and point it to the folder in which you copied the .inf file from the PSR 800 CD.
12-Install this Driver. An alert screen will pop up to warn you that this is an unsigned driver, Select install anyway. This will load the unsigned driver and allow it to work with EZScan
13-Check to see if it is working by Starting EZScan and selecting Scanner SD Card and select to set the Real Time Clock to Computer time. If it does it successfully you are good to go.
