As others have noted there seems to be issues for many users when "upgrading" to 7.0.1473, in my case:
Win XP Pro x64
DEP Always On
Microsoft EMET
Spybot S&D (but only the browser immunisations, not normally running)
Comodo Firewall (only the firewall, no defence+ or AV)
As with everyone else, the install seemed to go well and I rebooted. The first indication that something was wrong was that there was no activity on my 3.5" FDD, normally I wait until it does a little rattle before clicking on my user account.
So I clicked on my user account and got my desktop background, but that's all, no start menu, taskbar or icons. After leaving if for 5 minutes I tried the old Ctrl-Alt-Del and was able to get the task manager up and selected restart but that had no effect, after another 5 minutes I did a hard reset and booted into safe mode.
I was able to uninstall in safe mode, though that was needlessly difficult as the uninstall screen is to big for safe mode, rebooted and reinstalled 7.0.1466 and once again everything worked.