your not supposed to be editing the .dat file.... all you do is change the file extension to .ess, then place your save in the respective folder with your other saves and open it as normal.

Note that if it freezes during opening the save you can just reload the save on 360 go to a home you own, take off every single item that is DLC related, so anything from dawnguard or any building materials from Hearthfire like clay,quarried stone glass etc.(if your not sure just put everything into the chest. after this close the box but stay inside your home (must be on the original disc not DLC related) save it extract save from USB/HDD change to ess and then load it up and it should work

You don't edit your regular save. Instead open the CON file and you should see something like savegame.dat. Extract that to your PC Skyrim file folder, renaming it with the extension as you discussed. Load the game , enter the appropriate console commands, save the game. Replace your original savegame.dat file with your new pc save file. This has now modified the regular save file. Copy the regular save file to your usb and load her up. Should work. Note previous posters comments on on dawnguard items. If you're still having trouble PM me and I'll walk you through it. Good luck.