When I open the Store screen from Steam, nothing is shown.
The most likely cause of this is Internet security and/or Firewall software.
Many customers have reported that the nVidia Network Access Manager has been known to cause this issue. This is normally installed with the nVidia Forceware motherboard drivers. If you have this software installed, please uninstall it from the Windows Add/Remove panel. After it has been removed and you have rebooted, you should be able to view the webpages that load from the Store screen.
If you continue to have problems, make sure to run a full spyware and virus scan. The problem may be caused by a browser hijacker or other malicious programs running in the background.
Also, test the issue in an external web browser (Firefox, Internet Explorer, Chrome, Opera, etc).