We had an instant hot water system installed and now if water is turned on downstairs we get no water upstairs this didn't happen before can you tell me how to fix this or why this would happen

Is it "Instant Hot Water System" or "Hot Water Recirculating System". Please, clerify...

What you probably have is simply a faulty director valve. It is near the top of your hot water tank, it shouldn't be that hard to find. Just replace that and you shold be fine. Good luck.