You haven't had to enter a registration number/letters for SH4 yet.... might be good news.
Maybe toss this idea out and
see what the guys think.
How about zipping up what SH4 mod files you have and move them someplace safe, and do an uninstall of SH4 through add/remove programs. Also remove Save Games SH4 folder in My Documents.... also any folders in your C:\a sub game folder.
Next run CCleaner (free) - Just a 'regular cleaning' with default settings.... the broom icon
https://www.piriform.com/ccleaner
Then remove all traces of Silent Hunter using Ccleaner again by cleaning your registry with Ccleaner (backup registry when it asks you), then try to install SH4 Gold fresh.
What do you guys think?????