Home network problem

[reddevil2]

I am studying for a CCNA certificate, I already have a CompTIA Network+ certificate. But I am bamboozled with this enigma.
I bought a router connected three PC's at home,and a printer to a cabled network all worked fine, could even print from every PC and transfer files, even connected my sons PS2 to the internet, . Then my son need to re-install his operating system . Now we have internet connectivity, but have lost the ability to transfer or print from the other PC's that are not directly connected to the printer.
Though the PC's run three different OS's cannot work out where I am going wrong.

 

[pendal1]

I'm assuming you're working with windows so I would check and make sure File and Printer sharing are tunred on and that the Client for Microsoft Networks is installed on all the PCs. Additionally, do you have all of the PCs in the same workgroup. Those are the things I would check first.