I bought a used fuji s3100 digital camera, and can't find the interface software anywhere. any ideas?

Sorry, did did not put in any fuse in this camera. When it does not start up, check the battery, if it still holds some charge and the contacts, both on the battery and in the camera. All contacts should be clean and shiny. Only clean with a dry cloth or cotton swabs. NO SHARP tools.

The S3100 uses xD Picture Cards.

Please visit fuji's website and search for downloads.

Here is the link to the fuji usa website
This has links to the quick start guide and the full manual.
Join the link to make one line in your web browser.

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http://www.fujifilmusa.com/support/ServiceSupportProduct.do?prodcat=789909
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If that doesn't work I found it by going to:
http://www.fujifilmusa.com/
Then under Support And Contact Center I found Digital Camera Software And Support and found S3100 under Finepix.

First, make sure that the camera is not connected to the USB port. Then, go through the menu to settings, and on the second page of settings, you'll see at the bottom a selection for USB connection. Just click the arrow until it reads "Web camera," exit, and then plug it into the USB port. :)

Btw, it is in the instruction manual (well, at least the pdf one) ... you have to dig for it though.

I BOUGHT ONE THAT WOULDN'T TURN ON, WITH THE CD ON EBAY FOR $5.50 PLUS POSTAGE.

http://www.fujifilmusa.com/support/ServiceSupportPartsContent.do?prodcat=789909
yOU MAY BE ABLE TO ORDER A NEW ONE, OR THEY CAN DIRECT YOU TO A SERVICE CENTER.

Try Fuji's website. I think the website is
http://www.fujifilm.com/products/digital/download/index.html

The cd you're looking for I think is on the 2nd column and 2nd row. Let me know if this helps.

I think problem is under the lid where batteries go a residue forms. like the same stuff that forms near your car battery terminals. ??

Only the manual will tell that- have got it- if not in book form then on the disk? You could get on the the Tech Support Team at Fuji