I installed a new bathtub faucet and the only thing that comes on is the hot water. It's a single type faucet. It has a coupling like fitting that slides in and out and I believe that in order to adjust it you must turn the plastic piece underneath but I am having no luck with turning the piece. Any ideas or input?

Post photo... or give us brand/type/style of the faucet.

It is a delta monitor and I do not have a camera with me...

Does it look like this ?

http://www.savingsahead.com/pimages/1448C-74_PRODUCT_VIEW_1.jpg

No?

Double check your work:

1. Delta faucets come with dummy cartridge. You install the real cartridge up on finish. Make sure you put it in the correct way
2. If the valve has angle stops - make sure the cold water stop is open
3. Remove cartridge and flush the body. There may be debris
4. Observe the cartridge. See if it doesn't appear damaged ( there is a pressure balancing device inside. It may be stuck in hot side )

If nothting works - call Delta. They will send you new cartridge

I assume you have hot water in all other faucets in your house...