I have a moen single valve shower. I'm not getting any hot water or cold pressure now. The problem started not getting any hot pressure... went out bought a new cartridge,now I get hot pressure with no hot water and no cold pressure... what am I doing wrong here.please help I need to take a hot shower

Bought a new cartridge was your first error, they are free from Moen if you call their warranty department. You have a clogged inlet and I think you also installed your new cratridge upside down and reversed the problem. Shut off your main, remove the cartridge, cover the opening with a towle held tight, turn the main back on for about 10 seconds while you get a bit wet. Insdpcet the cartridge for debris and install with H/C on top by the clip.