Charles won't start with "Failed to find Java VM"
Charles uses Java so you need to have a Java Runtime Environment installed. You can download Java from Oracle.
If you are using the 32 bit version of Charles you must have a 32 bit JRE installed, and vice versa if you're using the 64 bit version of Charles you must have a 64 bit JRE installed.
If you have the correct JRE installed and you still get a "Failed to find Java VM" message, please try reinstalling Java – if Charles can't find your JRE then it is likely that your registry contains some invalid details, which reinstalling will correct. Also note that Charles requires a JRE and will not run if you only have the JDK installed. When you install the JDK it will offer to install a JRE as well, so this is usually not an issue.