Hi Mike,
Is there a way to re-install updates?
Just delete the "updates.xri" file that you'll find on the "C:\Program Files\PixInsight" folder. The next time you launch the PixInsight Core application, it will detect all available updates.
An alternative is uninstalling PixInsight and reinstalling it. The procedure I recommend is:
1. Uninstall PixInsight. Select "Start > All Programs > PixInsight Platform > Uninstall"
2. Reboot your computer (shouldn't be necessary with Windows 7, but what you're experiencing is very weird anyway)
3. Install PixInsight 1.8.0.1015 RC7 again.
4. Launch the PI Core application and apply all available updates.
Let me know if this helps you.