I loaded several mp3 files and some video files on my sd card when docked in my pc....but after installing it in the phone (8100), the folders in music and such from the card show nothing, help?

You have to unplug the usb cable from the phone first, or else they will not show up. If you already did that, sorry for the spam.

they have to be in a specific folder

BlackBerry\music
BlackBerry\pictures
BlackBerry\videos
BlackBerry\ringtones

in order for the media player to pick them up