Every sim in town is gone

@Hokzi  Unfortunately, if your backup save is also corrupted, there may not be much you can do.  This is why so many people use "save as" instead of "save" to generate new save files—I currently have about 30, which is admittedly too many but definitely makes me feel more secure.

Before you declare this game a total loss, though, it might be worth trying a couple of troubleshooting approaches.  The first thing to do is to delete your cache files from your TS3 folder in Documents.  For reference, they are:

CASPartCache.package

compositorCache.package

scriptCache.package

simCompositorCache.package

socialCache.package

Then load the game again and try to reset the sims.  (If you're playing modless, this is the only in-game step that I can think of.)  Hit crtl-shift-c to open the cheat console, then enter "resetsim *" (that's an asterisk) without the quotes, and every sim in town should be reset, if they're somehow still there.  You can also try one sim at a time, with "resetsim firstname lastname."  Save as with a new save name, quit, clear the caches again, and reload.

If this doesn't work, you can also try pulling your entire TS3 game folder out of Documents.  When you launch the game again, a clean folder will spawn with no content.  Copy your save to this folder (you can right-click to copy instead of just moving it, and that way, you'll have a spare) and load the game.  If the sims don't show up in town, try the reset cheat again, save as, quit, clear the caches, and reload.

If these steps don't help, though, I'm not sure what else you could try.  Unfortunately, sometimes saves glitch out, and there's really not much we can do to recover them.

Thank you so much for trying to help!

I tried the first one, and it didn't work, and I tried the second one, but when I try to enter the family(which by the way doesn't have a family photo, if that makes sense, it just shows the basic family-picture with outlines of a family), but it says "Cannot load this save game. It may have been saved with expansion pack data that is no longer present on this system". I have all the expansions, so I'm confused by this. 

Edit; could this be because the save is in a CC-town?

Edit 2; I copied the CC-town into the new save, got into the town and all the houses are still empty. I'm just going to start over, thanks for the help though!

@Hokzi  I'm so sorry to hear that you couldn't recover your save.  On the subject of cc towns, I couldn't begin to tell you what bugs and glitches you might run into without knowing which town you're using.  But larger worlds are harder to maintain than smaller ones, and lots with a lot of items (as in, maybe over a thousand, but it depends on your system) can cause trouble as well.  There are also routing issues associated with some CAW projects, although others are done better than most EA worlds.

If you want to chat with or get advice from active builders and the players who use their work, you might like to check out the Sims 3 forums builders section.  The people over there (and in the help center on the same site) will also be able to offer you tips to keep your game as stable and corruption-free as possible, so that this doesn't happen again.

http://forums.thesims.com/en_US/categories/builders