Java Won't Run Launcher

There are situations where Java can be installed, but stops running the Launcher or other Java applications. This usually occurs because the system path has been reset, or some application has removed Java from the system path.

Important Note:
These instructions are considered advanced and if you're uncomfortable, please contact someone to assist you. Because these steps involve the Windows system path and Windows system variables, it is possible to cause serious issues with your Windows install. Please be advised that these instructions are provided without warranty and you follow at your own risk.

Official Java Docs 
http://docs.oracle.com/javase/tutorial/essential/environment/paths.html

General Description
The system path is a list of folders that Windows should search if it needs a program. For example, c:\windows\system32

To resolve this issue, there's two steps.
1. Find where Java is installed
2. Check the system path
3. Update the system path

Finding Java
1. Java is usually installed in C:\Program Files\Java\jre6\bin or C:\Program Files\Java\jre7\bin
2. If you see multiple folders, you want the one with the biggest number at the end.
3. Take note of this folder for when you are updating the path variable (below)

Checking System Path
Finding the system path varies between Vista / Windows 7 / Windows 8, and WindowsXP.
 

Windows Vista and Windows 7

1. From the Desktop, right-click My Computer and click Properties.

2. In the left column, click Advanced System Settings.

3. In the System Properties window click the Environment Variables button.
4. Scroll down the System Variables list and select the Path variable
5. Click Edit

Windows 2000 and Windows XP

1. From the Desktop, right-click My Computer and click Properties.

2. The System Properties window will be displayed. Click the Advanced tab along the top.

3. In the Advanced section, click the Environment Variables button.

4. Scroll down the System Variables list and select the Path variable
5. Click Edit

An example path is:
C:\Program Files;C:\windows\system32;C:\Program Files\Java\jre7\bin

Check the displayed text for the Java path, as you determined in the Finding Java step above. If missing, add it to the end and make sure you have a semi-colon between your new entry and the Java path (see above)