Reinstall Mac OS X with the BSD Subsystem.
The BSD Subsystem is installed by default as a part of Mac OS X. You must have intentionally deselected it to experience this issue for this reason. If you did a standard (non-custom) installation, then you should troubleshoot further and search the Knowledge Base for other related issues. You should also make sure that your network connection is still active, since a lack of network connection may also prevent Windows File Sharing from working.