Faulty Faucet?

We have a mixer faucet on our large master bathtub. A couple of weeks ago the cold water stopped working. I turn the knob for the cold water and nothing comes out at all - it just turns and nothing happens. The hot water still works just fine. All other waters supply to our showers, toilets etc still working ok too.

Any suggestions on what could be wrong with the cold water and how I can fix it?

Thank you!

 

It's really hard without either a picture or the brand and model. If it is a cartridge, you may need to replace it. If it has a valve seat, the washer may have dislodged and is plugging the outlet. It could be a $0.10 repair (new washer), or even free, as some manufacturer's warranty their cartridges for life. Or, you might have to replace other parts which aren't covered.