My friend is acting non-responsive

Okay, just 5 days ago my friend was his happy and cheerful self. Today and friday he was depressed as a dead person. I asked him what was wrong, and all his said was this:

Did someone close die? "No.."
Did you lose something? "That's not it..."
Did you turn emo? "what?...never mind..."
Are you feeling ok? "yeah, im fine..."

Me: "Please don't comit suiside..."
Him: "Don't worry. I won't."

5 minutes later

Him: "mmm...I'm so depressed..."

Help!

dont let him be alone as tihs could be a major problem and by the way keep him away from sharp objects and rope

if he asks you what you are doiing say nothing im just worried about you And then Youu can take it from there

find stuff 4 you 2 to do together so he will feel better.

Could just be something going through his mind right now, Maby strong feeling of guilt.