Open My Computer - Tools - Folder Options - View and scroll down to Use Simple File Sharing and tick the box (if not already ticked).
Then check that the firewall will allow access from the other pc. Often you have to tell a firewall that a particular computer is a "friend".
You may need to know the IP address of that computer. Click on the network icon on the taskbar, then open Support. That is the address that should be a "friend" in the other pc's firewall.