Without being there it's impossible to be certain, but based on what you've said I would be looking for a loose connection (or possibly more than one).
With loose connections, the voltage drop across the loose connection increases as the current draw goes up. This usually means lights get dimmer and any loose connections get warm, so it's entirely possible there is heat damage that will require attention (and it goes without saying that it's a potential fire risk).
But, this is based entirely on the very limited information you've provided and I could be wrong.