When sharing the entire content of a partition with other computers on your network, you might see that it is listed as shared but in fact it cannot be accessed. Other users trying to access your partition might receive the following error message: '\\ComputerName\Partition is not accessible. You might not have permission to use this network resource. Contact the administrator of this server to find out if you have access permissions. Access is denied.'
In this tutorial we will show you how to solve this problem.
Our solution aims to solve only the error shown below. If you receive other messages, it might not be an applicable solution.

Error Message
First, open Windows Explorer and right click on the partition which you have shared. Click Properties.
Partition Properties
In the Properties window, go to the Security tab. Here you will see a list with the defined groups and permissions. If the group called Everyone is not listed, then you need to add it. If it is listed, you need to check the defined permissions and set it to at least Read & execute. To add the group, click Edit.

Partition Properties
Now click Add.
Partition Properties
In the 'Select Users and Groups' window, type 'Everyone' and click OK.
Partition Properties

In the Properties window, click OK.
Partition Properties
Now you will see a window titled Windows Security. Wait until it disappears.
Windows Security
From now on, your shared partition will be accessible from other computers.


source: www.vista4beginners.com