@Experteece what is the installation and operating system? I would suggest to try the one where you would just download the zipped version and try to start that.
(if your system is Windows)
From my experience if KNIME would not start you should check the amount of memory rserved for KNIME. How much is that? I would recommend start with half of your memory and increase that to 2/3.
You might want to check out further hints about KNIME performance and problems.