Mono - Develop not working?

Open Start -> All Programs -> Unity, then right click on "MonoDevelop", select Properties. In Properties window go to Shortcut tab and in "Target:" textbox paste this: "C:\Program Files\Unity\MonoDevelop\bin\MonoDevelop.exe" if you have 32-bit Windows or "C:\Program Files (x86)\Unity\MonoDevelop\bin\MonoDevelop.exe" if you have 64-bit Windows. Double quotes are necessary! This will work only if you have Unity installed in standard path. In other case you have to find MonoDevelop.exe with Windows Search and paste "Your path to MonoDevelop.exe" as target. If it won't help, just reinstall Unity.