Sharing files through an ADSL modem router

Hello sir,
I have connected my PC to a ADSL2+ modem router via usb and my laptop via LAN port.
Internet connection is shared,no problems.
my PC's ip address is 192.168.1.100
my laptop's ip address is 192.168.1.101
when from laptop I ping 192.168.1.100 , I get reply.
but when from PC I ping 192.168.1.101, I get Time-out.
I have played games through LAN with these two computers and there were no problem. the servers were created and recognized each other.
But when I want to share files, I can't. I can see both systems in Workgroups,but from laptop(where I get reply from pinging pc) I can open PC's shared place(but password is required and I don't know what is my password). but in PC I can't open laptops shared place(where I get time-out by pinging).
What is the problem and how can I solve it? these are both my personal belongings and I'm at home.
Thank you