Fluval 180L T8 Light Not Working - Idea's Plz

[clivealive]

hi,
my sons just got a second hand tank and its a fluval 180L  with T8 lights
he's got new tubes and one light works and the other doesnt.  (doesnt flicker nothing)
he knows both tubes work as he has swapped them over.
assume there no wrong ways to fit them ?
could it be something simple
any thoughts.

 

[star4]

I have a fluval 125 but dont know the 180 model so mine maybe different. If you look behind the light tubes you should see a white cap - inside here is a starter, it could be that gone.

 

[clivealive]

thanks