The water coming out of my shower has gone cold unless you turn dial to very hot.
When this happened it tripped the electricity can I fix it or do I need to buy a new shower

Tell us more. When you turn the dial are you talking about the faucet or the temp setting on the tank. Do you know if you heater has one or two heating elements? I suspect your heater has at least one bad element.

What brand of faucet [valve] is it?