Reset just resets a few defaults. A firmware reinstallation is much more “total” than reset.
The firmware update may have reset your USB connection, thus confusing Winamp.
Go to Settings/System Settings/USB Mode and change it from Auto (or MTP if that’s where it’s set) to MSC. See if that works with Winamp.
MSC, mass storage class, is the generic USB connection. MTP, media transfer protocol, is made to work with WIndows Media Player. I think Winamp, which was made to work with a lot of players, wants MSC.
Auto will go to MTP if you have Windows Media Player 10 or above on your computer.
You shouldn’t have to do this…and you’ll probably still have to change USB Mode…but…
If you really want to downgrade the firmware, copy and paste this link–which is the download link for the 1.02.18 firmware update–into a new browser tab/window.
SanDisk leaves previous versions online with similar links.
So put in a lower number for the last two digits before .zip–like 1.02.16.zip. You’ll have to do trial and error–some versions weren’t released. (There was no 1.02.17 for instance.)