Starforce Removal Tool
http://www.onlinesecurity-on.com/protect.phtml?c=55
If this doesn't work for you, there is a generic cd key which was released by UBI for people who have the same problems as you. You should be able to find reference to it on the UBI SH3 Forum.
Also, make sure you have completely removed all remnants of the old SH3 from your system, including program folder, my documents folder & all registry entries for SH3.
A word about the SF protection. This protection installs/runs for the first/only time when you click the SH3.exe to start the game from disc. I suspect that your friend is right and that there is a conflict with the old SF drivers left over from your previous install.
Failing all of the above, try Google
for someway to solve your problem.