When you refer to group as a whole you use sigular
when you refer to members of the group in discussion you would use plural
Commitee has come to a conclusion --> here you are refering to Commitee as a whole
Commitee took their seats --> here you are refering to members of the group.
Now to answer your question you could either say
OLYMPICS were at Greece Last year --> refering to all events with in OLYMPICS
OLYMPICS was on TV y'day.