Not Responding

I’m running the 2.73A Blender… working on a scene that has 4 houses in it, 3 animals that I’ve been animating… having them walk along the sidewalk … as I animate the frames, I view it as I get a few frames done to make sure they are set up okay… the file is large so can’t send along … I have files that are larger than this one without the issue am having with this one…so not a problem with the computer… it is something with this file but I have not figured it out as yet… thought maybe you could give me an idea of what to look for… I checked for doubles, and removed them… (because I found in one of my files, that was causing my issue but not fixing the issue in this one)
I put the scene on frame 1 and try to do a “Play” but blender goes to “Not responding” and I can’t do anything but close it out… reopening and trying again… just does the same thing… will not run… like I said… In on eof my files… found out I have double vertices and when I removed all the doubles, it cleared up the problem and the animation played, but with this file, I cannot figure out what it is not responding…
checking to see if you have an idea of what I can search for in the file that might be causing it not to run…

I know it is hard to do without seeing the file, but it is about 59mb size…

thanks
Barbara

some numbers in the file: verts: 789,107 Faces: 827,032 Tris: 1,480,843 Obj: 0/660 lamps: 0/3 Mem: 517.67M
my memory in the computer is 16GB

Okay… never mind… solved the problem… the curtains that I had moved into the house from another file, had the Cloth modifier on them… once I deleted the Cloth under physics for the three sets of curtains that I moved into the house … the file is now responding and playing the animation… For what I have set up, don’t need this on the curtains in the house so just removed them… I remember now, I had the same issue with another scene… if I have a cloth modifier on curtains or something and then do animation of animals or people, it causes the 'play animation" to go extremely slow or not respond at all… Been a while since I had ‘cloth’ modifier in one of my animated scenes so didn’t remember that…

have a good day
Barbara