Windows BSOD when all cpu cores enabled

You have a "Nehalem" microarchitecture Intel CPU, you have Windows Server 2008 R2, and you haven't installed the hotfix.

Further reading

Microsoft blames Intel.

• Ben Armstrong (2009-10-16). Hyper-V Hotfix for "0x00000101 - CLOCK_WATCHDOG_TIMEOUT" on Nehalem systems. MSDN.
• Microsoft corporation (2010-11-23). Stop error message on a Windows Server 2008 R2-based computer that has the Hyper-V role installed and that uses one or more Intel CPUs that are code-named Nehalem: "0x00000101 - CLOCK_WATCHDOG_TIMEOUT". MSKB 975530.

Intel blames Microsoft.

• Intel corporation (2010-07-12). Stop Code 0x00000101, CLOCK_WATCHDOG_TIMEOUT Error in Windows with Hyper-V. CS-031717.

Always check the doco provided by the manufacturer before coming to SuperUser.

• Microsoft corporation (2011-10-26). Hyper-V Update List for Windows Server 2008 R2.