Presence of Online Stores in Windows Media Player in Windows 7 is one of the salient features. One can use Windows Media Player to find and subscribe to music, video, and radio services, as well as other types of content from online stores.

To find Online Stores in Windows Media Player, open Windows Media Player in Library mode. If you’re in Now Playing mode, click the Switch to Library button.

Now in the left pane of Windows Media Player, you will get Online Stores.

Sometimes you will find that Online Stores are not working in Windows Media Player and clicking the downward arrow you are not getting Media Guide option either. We are located in India and we were getting "No Available Online Store" on this system.

Now to get back the Online Stores functionality as well as Media Guide option we did the following:

Open Control Panel

Open Region and Language

Click the Formats tab

Changed it to English (United Kingdom) from English (India)

Click OK.

Now Online Stores is working and Media Guide option is back.

Changing the Format to a different country eg. UK/US helps this.