Hi Welcome to FixYa!
Have you already installed the drivers for your computer? If not yet, it could be the reason why you are not able to use your wifi.
Follow these steps so that you could know what to do next:
1)check the device manager in Windows:
A)if you are using Windows 7 or Vista:
-click on Start, then on the searchbox, kindly search for Device Manager and open it.
You should have something like this:
B)if you are using Windows XP: click on start>run>type devmgmt.msc and it will open the device manager Window.
2)If you will find a category that says Other Devices, kindly look for a item that says "Network Controller" if you find it, it means that the Wifi adapter on the comptuer is not yet installed. All you need to do is insert the drivers disc CD if one came with the computer when you bought it. If not, you could try connecting the laptop to the modem directly using a cable and download the driver from Lenovo's support website: www.support.lenovo.com
3)If you still cannot connect with a direct connection, the Ethernet adapter could have been not yet installed also. You could also check it on the Device Manager window and look for Ethernet Controller under Other Devices. or check the category Network Adapters and see if the Ethernet Adapter is installed.
4)if the drivers are already installed, you can try contacting your Internet Provider or call Lenovo's Technical Support Team.
hope this would be a big help!