The cold water is not working in my upstairs shower. The cold water works fine at all other points in the house.

I replaced the Moen cartridge in the single handle unit, but the problem still remains. After the new cartridge did not work, I turned the water on without the cartridge in the faucet and found only hot water flowing.

There are two sinks in the same bathroom hooked up to the same pipe. Both of them have cold water.

Does anybody have any suggestions??

I turned the water on without the cartridge in the faucet and found only hot water flowing.
Well you can't fault the cartridge. You have a blockage downstream from the valve that shuts the cold water off. Try this. Shut the water off at the house shut off and remove the stem and washer assembly from the cold water (right hand) integral stop on the valve body. Run a stiff wire down in the opening both toward the valve and back into the supply line. Now have someone turn the house back on, count to five and then turn it off. Did cold water come out of the open stop? Let me know. Good luck, Tom,