Can i reprogrammed a bad ecu or should i buy a new one

Through what testing did you arrive at the conclusion that your problem lies with the "ecu"? What makes it "bad"? I would suggest that control modules are extremely infrequently faulty. The cause of concern is likely related to another component or wiring. In fact, have you started by checking the battery? The state of charge and the ability to hold a load? Have you checked battery cables for proper fitment and ensure that they are free of corrosion? This is where I would look first. Your powertrain control module is almost certainly not a problem here.