Lenovo has identified root cause for an issue that causes Lenovo ThinkPad systems with Broadwell and Haswell chips to hang or freeze at OS boot after upgrading the BIOS to versions released in August 2016. This is known to occur on ThinkPad systems running Windows 7 and Windows 10 installed via legacy Windows 7.
Root cause was identified as a conflict between the BIOS and a feature in ThinkPad Power Manager for Dynamic Brightness Control. This setting is disabled by default, so only customers who enabled the feature would encounter this issue.
Lenovo is working to provide updated BIOS that resolve this issue.
To check if an updated BIOS has been released for your system, please visit support.lenovo.com to view the most recent BIOS version made available.