You need to change your usb mode. If you loaded the files in MSC mode you cannot see them if you are connected in MTP and vise versa. So try going to the settings menu on the fuze and go down to USB mode, and change it to MSC, plug it in and see if you can see the files, if not then go back and change it to MSC. There may be a way to change it with out disconnect but I am not sure how.
If you upload the songs in one mode, you cant view them in the other. There are three modes in which a fuze connects, Auto, MTP, and MSC. To view your songs, put your fuze in one mode and search for them on your computer. If that doesnt work, try the other mode. You should find them. (Auto mode is just auto detect for MTP or MSC)
I havent found too much of a difference between the two as far as quality, ease, blah blah. Personally I keep mine in MTP mode just because it is easier to upload the album art. Plus, My Computer->Right Click on Fuze->Properties shows the battery charge level. That came in handy when I had my hands on a Fuze that got stepped on. Cracked LCDs are no fun.
Auto Detect has a peek at the installed OS on the host computer, and connects in MTP if available. I find the feature quite useful, as I often use the Sansa to transfer diagnostic data, in MSC mode, and keep my music separated, in MTP mode.