Hello,
In regards to the issue please use your OS disk to access the Vista repair tools. Even for those without an OS disc, Vista has repair tools built in. To access them, boot the computer, but when you see the Microsoft (C) with the moving lines, hold the power button until it shuts down. Turn on the Windows and select Windows Startup Repair option. When it loads, cancel the scan it starts (it wont find anything anyway), and choose the text on the bottom that says something like Show advanced repair options. which should get you to a command prompt option. You can also get to a command prompt via holding down, or repeatedly clicking, F8 as the computer begins its reboot. - select safe with command line.
Note that this may take a few runs through the reboot F8 routine which is why the OS disk route - if your machine came with or you later bought such a disk - is preferred. Once you have the command prompt the need is to remove a file pending.xml that is causing the forever loop.
If it still hangs on "Stage 3 at 0%" with reboot and hang again forever cycle continuing, just do a repeat of the F8, and select safe mode w/networking. Stage 3 may well continue and finish normally.
Please let me know the status of the issue.
Thank You.
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Anupama
Parallels Team