I'm running Windows 7 Ult x64 with SP1rc installed the day it became available. My system is a dual Dell i7 with 12 GB of DDR3 RAM (a Studio XPS Desktop 435MT). Video card: ATI Radeon HD 4800 Series (4850), most recent drivers installed, reinstalled, etc., ad nauseum. Beginning Monday, November 8, 2010, after I installed a definition update for MS Security Essentials (1.93.1441.0), all attempts to reboot result in the dreaded Black Screen of Death following login. The only work-around has been to power cycle, enter safe mode, and do a system restore. I did the customary edit of HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\Shell when in safe mode. I've applied the http://www.prevx.com/blog/140/Black-Screen-woes-could-affect-millions-on-Windows--Vista-and-XP.html fix--all of this to no avail. Scans with Security Essentials and Malwarebytes' Anti-Malware disclose no problems. I suppose the real solution in a new install, but on this box, it is going to be painful--discomfiting in the earlier sense of the word. M A Reeds MD PhD