Modem working but no signal being received by laptop

Hi
We have been having issues with our modem until today when my partner decided to unplug the modem and move it to another spot. Once he did this, the signal from the modem stopped being picked up even though the modem is working with all it's lights on showing that it's connected to the internet. I have moved the modem back to it's old spot and it's still not working and have also tried another modem. It picked it up briefly and then dropped it. Can anyone tell me why this is happening and how I can fix it?
Thanks