Problem after battery replacement

[Cholas]

My Go Live 1005 is seven years old and with a dead battery and so I decided to replace the battery following guides on YouTube. Everything has gone fine except when I attempt to re-close the unit because the on/off button somehow locks itself and the Tom Tom ceases to operate. Until the point when I snap the unit closed everything is fine - I have connected it to my pc and downloaded the latest updates but the moment I snap it closed the on / off button "locks" and won't function. Clearly I'm missing something here but for the life of me cannot figure what exactly but then I am not particularly technically proficient and so any advice gratefully received. Thank you.