Windows may hang during boot if a USB storage device is attached immediately after EFI POST

Applies to: Windows 7 EnterpriseWindows 7 Service Pack 1Windows 8

Symptoms


Consider the following scenario:

  • You have a UEFI-based PC running Windows 7 or Windows 8 x64.
  • After powering on the PC or rebooting, you attach a USB mass storage device immediately after the EFI firmware POSTs and before the Windows logo (or OEM boot logo) appears.

In this specific scenario, Windows may hang at the "Starting Windows" screen on Windows 7 or the boot logo screen on Windows 8.


Cause


Because this potentially bootable device is not initially connected, the Windows Boot Loader will try to open the protocol interface and map it during startup. However, when it is time to close the protocol interface and unmap the device, the Windows Boot Loader may incorrectly unmap additional memory regions. This can lead to an access violation and a system hang.


Resolution


To workaround this issue, try either of the following steps:
  1. While the system is hung at the "Starting Windows" screen (or Boot Logo screen for Windows 8), power off the PC and power it back on again. To force a power off, you may need to hold down the power button for 4-5 seconds.
  2. Attach the USB mass storage device before you power on the system.