Well, there are many posts on this subject, i will insist only on HOW to do it:
* beacuse you have the Windows Domain Server Controller , or NOT
* or personal computers, joined with hybrid networks
* or home-based, neighbourhood networks

So, to SHARE you do as below keeping in mind four things
A. The “Shareability”
B. Who is supposed to do and what to do
C. The Ownership of the Files
D. The Security of the Files
if one is missing you cannot access the folder as you want

1. Please navigate to the target file/folder.
2. Right-click on the file/folder and choose Properties.
3. Click the “Security” tab and see if your current user is listed in the “Group or user names” list. If not, please click Edit-> Add button, type the name of your current user in the “Enter the object names to select ” box, then click “OK” to add this group.
4. Select the user from the list and then check the “Allow” checkbox next to “Full Control”.
5. Click the Advanced button and click the “Owner” tab. Then, press “Edit” button.
6. Select current user from the list and check the “Replace owner on subcontainers and objects” checkbox.
7. Click “OK” to save changes and wait for Windows 7 to transfer the ownership of all the objects on the partition.
8. Click OK again to save changes and exit the Properties window.
9. Test the issue again.