a bad battery could cause this issue,get the battery tested,could be a cheap fix,if the battery is faulty it can become resistant to current flow,affecting the current the power steering needs,even though the car starts ok there could be an underlining problem,if that does check out ok,its most likely the the power steering unit ecu,or motor,connections,loose fuse,corroded wiring/connections.theres loads to check,and i doubt its the rack.