Do I need a new MP3 or is it fixable?
Hard to say without knowng more details. Have you tried scrolling both by turning the scroll wheel and pressing and holding the up/down/left/right buttons?
More information about what is going on (or not going on) would be helpful. 
Sometimes I can’t scroll up and down and where up/down/Left/right , home and power/hold buttons work but sometimes scroll for volume or scroll to hear a different album or artist
Do you carry it in your pocket a lot, or it is subjected to dusty conditions? You may have lint or other dirt or schmutz underneath the scroll wheel. Has there ever been any Coke, soda, coffee, etc. spilled on it to where it might have seeped under the wheel hindering contact?
This is a fairly common thing actually. You might want to try some of the cleaning suggestions in the discussions found by searching the subject:
