chassis fan stopped working

[Plutoburn]

I've noticed recently my case fan was rotating slower and slower, and now it just stopped working all together. When I touch the center of the fan, where the powersupply wiring go to, it felt quite hot, so I can rule out no electricity, what could be the problem and what can I do to fix it?

 

[Plutoburn]

Could it be caused because I leave the case's side panel open all the time?