I had a similar problem, and it took me ages to solve.
it turns out that the order you turn on your computers matters. If you created your workgroup on the main PC then switched it off, then the next day you turn on the laptop before the PC this can happen.
My advice is to turn of the secondary PC and laptop. Create a new wokgroup, you can give it the same name as before. Then turn on the next computer add the workgroup again and so on.
This should fix it. Also you should go into your router settings and fix the ip address of each computer (not your external ip address that the ISP give you)
typical ip address will be 192.168.1.1 for the router then the next PC to be switched on will have 192.168.1.2 the next 192.168.1.3 and so on.
If these are added dynamically this is where turning your computers off and on in a different order messes things up.
You should force your main pc to have 192.168.1.2 your next pc to have 192.168.1.3 and your laptop to 192.168.1.4