Hi there FNAFROCKS,
I know how to fix this, I have a little experience with mods, and I can try to help!
If you go to your .minecraft folder ( click me if you dont know how to find! ), copy and paste your folder called "saves" if you play singleplayer, a single file called servers.dat and, if you use texture packs, copy the "resourcepacks" folder to your desktop in a folder called "backup". You might wanna copy any other important folders you might have there (i dont think you will have though) Then, delete your .minecraft folder, delete minecraft launcher, then reinstall minecraft from minecraft.net . Launch minecraft. Then, go back into your .minecraft, copy the contents of the "backup" folder into the .minecraft (making sure you delete the new servers.dat, "resourcepacks" and saves folder that are currently in .minecraft) then launch minecraft again. Whoopee! All back to normal!
By the way, to get started with modding, use the "Technic Launcher(click me!)"
Good luck!
xAppleYT
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xAppleYTI'm a geeky Minecraft player, I also play a few steam games aswell
Glad to help Anyways, sub to me on youtube by clicking here! #Grapple!