Here is a step by step instruction to use a laptop as WIFI Router and access Internet through it on any other WIFI enabled deivce in ad-hoc mode :
1. Go to Start, Control Panel, Network Connections. Right click the wireless connection (it should be called “Wireless Network Connection”) and select properties.
2. On the window that will show up, click on the Wireless Networks tab. Make sure that no wireless networks are being listed under "Preferred Networks". If you see networks there, remove them one by one.