Today I encountered a volume-licensed Vista box that had not been activated for more than 180 days.  I was under the impression that Reduced Functionality Mode (RFM) had gone away with Service Pack 1, however when I attempted to log into the box, I was greated with an activation dialog box, and clicking cancel returned me to a log on prompt.  Here's how I got back around the problem...

• From the Activation dialog, click on one of the Help links.  This will pull up the Help and Support window.
• In Help and Support, do a search for "command prompt".  One of the returned links will show you how to open a command prompt, and will provide a link to do this for you.  Go ahead and open the command prompt in this manner - while I was in this activation mode, I was unable to use Ctrl+Alt+Del to pull up Task Manager, and had to get to a place where I could actually do some work.
• If you need to connect to a VPN in order to access your company's KMS server, do so now.
• In order to manually activate Vista from the command line, you have to run slmgr.vbs from an elevated command prompt.  How do you launch an elevated command prompt without right clicking on an icon to launch a UAC prompt?  Here's a nifty trick:
  • Run "control schedtasks" to bring up the Task Scheduler interface.
  • Create a new task to run cmd.exe without any triggers.  Also make sure to check the option for "Run with highest privileges" on the General tab.  This will set the task up to run with elevation.
  • Right click your newly created task and click Run.  Lo and behold, you've got a command prompt running with elevation!  Note "Administrator: taskeng.exe" in the title of the command prompt window.
• Now that you are elevated, run "cscript slgr.vbs -ato".  Assuming this volume-licensed copy of Vista had been previously activated, you should now be re-activated.
• Log off using the "logoff" command, and then log back in.  At this point you should be staring at your desktop once again.