Hi, my name is XXXXX XXXXX I have been in the plumbing and plumbing repair field for 20 years. I will be glad to help you today. If it is no longer earthed that will make a difference. Yes do fix the earth wire. Also if you did not flush it before turning the water back on then remove the shower head and clear any debris and check the inlet filter.
Did you flush it before turning the water on?
Almost certainly there is debris that has reduced the flow. If you remove the inlet pipe there is a screen there that will have debris. When you get the earth wire fixed that will help also. If you remove the shower head or sprayer is there more flow without? Also may be an airlock situation.
I would first start by repairing the earth wire and check the inlet. That is the most likely to cause issue.