If you installed win7 clean without using the Lenovo recovery win7 image then you are missing ALL drivers. Goto lenovo support and download and install all drivers. Lenovo used to have a tool that did this for you. Suggest you CHAT lenovo support and use this tool. Teh drivers you need to install are not intuitive, for example AMD ACHI drver was needed for one of my lenovo laptops on a clean build.
Lenovo will sell you a DVD with the original lenovo build for about $10. If the above procedure is too hard just call them and order the DVD. Make sure they send you the exact right win7, your BIOS is tatooed with your win version and serial #.
finally, microsoft security essentials is free and mostly works. run this if you are not using a comercial anti-virus.