JabRef relies on Java, and there is no way to use JabRef without it. If you have admin rights on your PC, you can install Java on your own (it is also possible to install java without admin rights, but that’s more involved - please google it). What might also work is that you may find a JRE that was installed as part of another program (e.g. an IDE or CAS). Then you can point the Java_HOME environment variable to this folder and everything should work. Or try to speak with your IT department and find a solution of how to enable Java for you (there are so many Java-based programs so that they are probably used to this kind of queries).