Why when I downkoad a hack it corupts my game.

at a guess
either because it is a bad hack, it is the wrong version for your game or it is conflicting with some other hack you have

Which hack(s) have you downloaded and how exactly have they corrupted your game? When you download hacks, you should make sure they are compatible with the combination (or lack of) the expansion packs you have. For example, several hacks that were made before the release of the Nightlife expansion pack are not compatible with it, and may cause serious problems in your game, but many of them have been updated since to be Nightlife compatible.

When I try to go to a property it just loads forever I think it is the mailbox hack.

Another one was strange. I would go to a property with a family and before I could do anything a disease would kill them all. Not sure what hack that was but it only started after I installed NL

The last hack is probably an old version of the insimenator. You MUST make sure the hacks you want to use are compatible with NightLife. If they aren't, you will get problems.