Here's what I would do:
1. Uninstall SH4
2. Reboot
3. Delete C:\Program Files\Ubisoft\Silent Hunter Wolves of the Pacific (if it remains)
4. Delete My Documents\SH4
5. Run a registry scan to remove any leftover entries (free scan at
http://onecare.live.com/site/en-us/default.htm (cleanup scan))
6. Install SH4 (including DX, skip Gameshadow if you want)
7. Patch to 1.2
8. Reboot
9. Defrag the hard drive
10. Game on!