From this post (http://answers.microsoft.com/en-us/windows/forum/all/brand-new-windows-7-computer-cant-open-explorerexe/b2876d38-177f-472a-b2e8-d155cc16ca68?auth=1) try these steps:
1. Click on Start
2. Computer > right click Local Disc (C)
3. Click on Properties
4. Click on Security
5. Select Administrators in Group or user names box
6. In Permissions for Users box, make sure you have full control