PC does not recognize my sansa

Did you try changing the USB mode?

There are two USB modes. MSC is the basic generic connection used by thumb drives, flash drives. If the cord and port are working, your computer should recognize it.

MTP allows control of the unit through Windows Media Player version 10 or above. XP shipped with WMP 9. It’s possible your office has WMP 10 or above and your home computer doesn’t.  So if the unit is in MTP mode and your home computer doesn’t have a newer WMPlayer, you get a problem.

So you could try updating Windows Media Player.

http://windows.microsoft.com/en-US/windows/products/windows-media-player

You could also install the MTP Porting Kit, whatever that is, which some people have reported can be useful.

https://www.microsoft.com/download/en/details.aspx?displaylang=en&id=19153

Note that your computer cares–but your Fuze doesn’t–about which USB mode transferred your music. If you sent files over via MTP, your computer won’t see them through the MSC connection, and vice versa.