Hi and Welcome. My Name is ***** ***** I look forward to assisting you today with your question.
I couldn't find any official drivers for Windows 8.1
I found this. Download the drivers from here --> http://www.fujitsu.com/global/support/products/computing/peripheral/scanners/scansnap/software/s510-setup.html
After installing, open the Scan Snap Manager app and does it recognize the scanner ?
Download this one --> http://bit.ly/1WS7pwW
Then open the Windows's scan app and does it recognize the scanner ?
That is because it an exe installation file. Can you download it from here --> http://bit.do/bPoAv
After installing it, connect the device to different USB port of your computer and let it install drivers automatically. Then use Microsoft's scan app to scan
I'm glad you got it sorted out. Since I didn't solve your issue, you can contact***@******.*** for refund.
Have a great day,