I had a Lenovo IdeaPad U350 downgraded to Windows XP. In order to make the wireless card work, you must install first Lenovo Energy Management utility, in order to make Fn+F5 buttons work. Also dont’t forget about the wireless switch located in the left corner of the laptop.
You will also see the third LED on, under your touchpad.
Wireless Utility U350
Wireless adapter type : Broadcom 802.11g Network Adapter
Hardware ID for Broadcom 802.11g Network Adapter : PCI\VEN_14E4&DEV_4315&CC_0280
Link to Lenovo U350 drivers & utilites : Link