When you setup the Network did you have both computers turned on? If not, that is the problem. As I had the problem and someone in PCA Networking Forum put me on the right track to modify it.
This should do it.
In the "problem" PC, check out this setting in the registry. Navigate to:
look for a DWORD "restrictanonymous" and see what the value is. If it is anything other than 0 (zero), right click the DWORD, select MODIFY and change the decimal value to 0 (zero).
A word of warning, there is a DWORD "restictanonymoussam" just below the one you want - DO NOT change this.
Close regedit and reboot the computer.