Hi, Check the APIC bypass de assert message bit. 0x5b bit3 I think you need to put there 0. There are some registers from 0x70 - 0x7f documented in the Programming guide only. 0x7c bit 3 is hypetrtransport mode for APIC put 0 there. And 0x77 bit 5 I dont understand what exactly it is. Try flipping it too. Rudolf