Assuming the tags are there, then you must pick a WPS file that displays them.
I don't know what WPS (You pick them, generally, by selecting "Browse Themes" from the "Settings" menu) you're using, but most of them will display ID3 tags. If you don't know, then I'd assume your mp3 files don't actually have tags. But, if you can tell us what Theme (or WPS) you're using, we can at least confirm that or rule it out.