I have been having these WiFi issues with my Z580. I had the motherboard as well as the screen replaced a month ago from an authorized Lenovo service center.However, after the replacement my laptop is unable to detect WiFi signals unless I am sitting right beside the router. I tried installing the required drivers for my Broadcom wlan adapter but to no avail.
Is an issue with the WiFi antenna which is somewhere behind the screen.I guess they might not have been fixed appropriately when the screen was being replaced!
I am using Windows 7 Home basic edition on a 64 bit system. The WiFi signals used to be excellent until I got the motherboard and screen replaced!