As has already been said, you have to make sure that the platform the mission was designed for is the selected unit within SCU.
3/4 loading - hmmm not sure on this, are you sure that you have instaleed everything correctly and in the right order etc. (not being funny, but it does happen). And ran all the required .bat file for EACH install prior to installing the next one.
As Markshot says, money is not an issue here. We will help you the best we can for free
Regarding a re-install. Do you still have the downloaded files saved on your PC or on a cd ? If so then a re0install is easy enough, if not then you'll have to re-download the mods again as during the install all of the graphic files needed to be imported into the required files are deleted.
Yes, i know you could just back up those files, but this is one of the things that may be causing your game to pause.