I tried copy and pasting the minecraft.jar 1.5.1 files into my.minecraft jar file inside bin, and after, I delete the updated one. Once I go to minecraft, it stays frozen when it says Done Loading. What am supposed to do, or what am I doing wrong?
How to downgrade Minecraft?
You are getting an answer from someone who constantly downgrades for various reasons.
Go to C:/Users/<Your User>/Appdata/Roaming and DELETE the.minecraft folder.
Run Minecraft.exe
Force Update.
After the update, go to C:/Users/<Your User>/Appdata/Roaming/.minecraft/bin
Delete the minecraft.jar file and copy your 1.5.1 file in. Make sure the new one is called minecraft.jar
Run Minecraft and it will most likely ask you to update. Select [No]
You might get on the Done Loading screen for a bit but let your computer sit for 5~ minutes. After that, if it still hasn't changed, contact Mojang for more information.
Also, make sure you download the official 1.5.1 Files.
Also make sure there are no /mods or /mod folders in your /.minecraft
Maybe try to use a program to downgrade it. I used to use MCnostalga but it doesn't work for me at the moment. I checked out the minecraft wiki for you:
http://www.minecraftwiki.net/wiki/Programs_and_editors/Specialized_programs
this link will show you different programs that you can use for minecraft including ones to downgrade it.