A new KB article related to Hyper-V was posted this morning.
You have a Windows Server 2008 R2 system with the Hyper-V role enabled. If the BIOS has been set to inject SMIs at a high rate, 11 SMI/sec for example. The system may hang during boot time.
As the rate of SMI injections increases, the likelihood of failure (system hanging) increases.
Cause
If an SMI occurs before all processors are ready to receive SMIs, Windows boot will hang.
Resolution
Reduce the rate of SMI injection in the BIOS to prevent a hang during Windows boot.