Windows 7 Wireless Configuration and Troubleshooting
Step 10: Modifying the Connection Mode
Click the Advanced tab in the window that appears.
In the Property list, click on the entry titled IBSS 54g(tm) Mode.
Note: Some wireless network cards do not support this option. If you do not have a IBSS 54g(tm) entry, skip directly to step 11.
After you have clicked on this entry, select 54g - Auto from the drop-down list on the right.
In addition, you may have another entry for Radio On/Off, make sure the value is set to On.