Minecraft Forums

have a look at this: http://www.minecraftforge.net/forum/topic/44986-new-launcher-how-to-start-forge/

and there is no point in reinstalling forge?

we can solve this manually, but it's a bit tricky.

1. check in your .minecraft/versions folder if the forge version actually exists. if not, install forge.

2. if it does, copy the name of the forge folder. in my case it's "1.7.10-Forge10.13.4.1558-1.7.10"

3. go back to your .minecraft folder and open the file called "launcher_profiles.json". use a text editor (not windows notepad or editor though! something like atom.io). you should see something like this.

4. now it gets a bit complicated. the first lines of my file look like this:

{
  "profiles": {
    "OptiFine": {
      "name": "OptiFine",
      "lastVersionId": "1.10-OptiFine_HD_U_C1"
    },

and now i insert my forge profile:

{
 "profiles": {
 "Forge": {
 "name": "Forge",
 "lastVersionId": "1.7.10-Forge10.13.4.1558-1.7.10"
 },
 "OptiFine": {
 "name": "OptiFine",
 "lastVersionId": "1.10-OptiFine_HD_U_C1"
 },

of course you need to replace "1.7.10-Forge10.13.4.1558-1.7.10" with what you copied in step 2.

5. save the file and try again!

if it doesn't work and you think you made some syntax mistake, post the file here and we will correct it. but be careful: the last part of the file contains your email adress and other stuff you maybe don't want to become public. so only post whatever is above "selected profile".

good luck

should've thought about the easy way