Another outside possibility.
Almost all laptops have some means of disabling the track pad if you plug in a mouse, the rest do this automatically. The most common method is 'Fn' + one of the 'F' keys. There is no standardisation of this feature, look for an 'F' key with a symbol of a crossed out trackpad or mouse.
It may be that a voltage surge when you switch on the charger is throwing this setting. If I do any serious work on a laptop I normally plug a mouse in, then my wife goes daft because I forget to switch it back to track pad when I am finished !