If you are using the Windows platform, then:
1. First navigate to the directory where Tomcat is installed. For e.g. I have installed Tomcat in C: drive, so my command prompt should read C:/Tomcat/bin> before i issue the start-up command.
2. Once you have managed to get the correct directory path onto your command prompt, just type 'startup' (without quotes) and press enter.
Follow the above steps and if you still face issues, please feel free to send me a PM.
help your PC help you best