home network

My computer crashed some time ago and since then I have been unable to link
my desktop and laptop computers with my network; they did connect
beforehand.
I cannot set up a home group despite both using windows 7 as ipv6 (I think)
is not available, can only use ipv4 (might be wrong words but 6 is not an
option).
My problem is that the desktop and laptop recognise each other on the
network but I cannot find a password that will enable them to share files
etc,.
When I open the Network and Security Centre I am asked to enter the password
to make the connection. I have tried the password for the router but that
does not work, I have also tried the password that was previously used for
the workgroup but that does not work either.
Does anyone know where I can find the "network password" that will allow the
network to function?
Thank you