I cant get hextech chests or keys

You can look at in the hextech crafting guide here to see the reasons why you would not be earning any chests or keys.

For chests:

• If you're playing a champion you don't own, you can't earn a chest.
• You may have already earned a chest with the champion you're playing.
• You may have reached the chest limit for the week.
• You can't earn a chest in a game if you leave that game.
• You may have been punished by a behavior system recently, meaning you won't be able to earn rewards from Hextech Crafting

As for keys:

The drop rate for key fragments is a curve, not a line. With each fragment you earn, the chance to earn your next one goes down slightly. This number resets roughly every thirty days after you earn your first key fragment.