There was a water main break somewhere in our town. We have low water pressure, but nonetheless we have water. Including the upstairs bathroom; sink and shower, but not in the toilet. A friend said it was because of the low pressure. Please tell me that is the case or otherwise I have a flushmaster water supply in the tank... could it be a problem with that?

Thanks for any help you can give.

Sounds like you have dirt insdie your fluidmater fill valve, here is what you need to do, Close the angle valve under the toilet tank, step 1 remove the cap step 2 remove the washer ste 3 hold your hand on top of the fill valve now open the angle valve to flush out the dirt from the fill valve, close the angle valve install the washer and the cap check now should be OK see the images below, Thanks.