You may have an object on that lot causing an error. Have you tried typing in
boolprop testingcheatsenabled true in the cheat box before entering a lot? That might bring up an error pop-up if I'm guessing correctly.

(I had this happen before, and it ended up being a custom dollhouse that had came with a downloaded lot. Might be different in your case, though.)
If the pop-up does appear, you can choose "Delete" and see if it'll load then. That option will get rid of the problem mod/object/sim on the lot. (no need to worry about the sims, though... they usually respawn upon exiting and re-entering the lot) But take note of what the pop-up says and the name and location of where the error log will be located. (almost always in your
Logs folder) You can always attach that particular log to your post and someone may be able to read into it a little more about the possible download causing it. :angel: