What to do when you've lost all hope in everything?

Some people turn to God but its important that it is believable and makes sense to you.
What I would do is try to understand what it was that started these feelings off in the first place.
True happiness cannot be attained thru material possessions.
I know this sounds cliche but help an old person cross the street (or just do 1 nice thing for someone). I bet it makes you feel a little better.

Pray. Find someone to talk to, and remember, no matter what situation you are in, there is always someone in a worse situation than you

Turn to Jesus.  He is our burden bearer, our shelter in a time of storm.
Matt 11:28-30
28 Come unto me, all ye that labour and are heavy laden, and I will give you rest.
29 Take my yoke upon you, and learn of me; for I am meek and lowly in heart: And ye shall find rest unto your souls.
30 For my yoke is easy, and my burden is light.
(KJV)