How do I get my abs light to go out after fitting new abs control unit?

My rover 75 developed an abs brake fault a day after hitting the foot brake pedal hard in a semi flooded road the abs system worked ok, until the fault lit up.Took it to a dealer they put it on their computer and told me the abs ecu was at fault For £850 they could sort it out !!!!!!!!!!!
Took it to a local guy fitted new ecu, still no abs braking and red brake light permanently lit and amber abs light permanently lit? so any idea's please!desperate to get this sorted!