I don't think there's any evidence for needing a new Java installation. I think this is much more likely to be a problem with the .jar path you're supplying.
If your maxent path is not in your PATH variable, and you're not invoking the command from the folder within which your maxent.jar is located, then you need to provide the full path to maxent.jar, e.g.,
java -cp C:\Users\John\Documents\software\maxent_3.3.3\maxent.jar density.Explain
You also need to provide the full path to the prediction (the .asc you want to interrogate), and the predictors (the folder containing the predictor grids).
A full example is:
java -cp C:\Users\John\Documents\software\maxent_3.3.3\maxent.jar density.Explain C:\GIS\maxent_output\species1.asc C:\GIS\all_preds_asc_baseline
If that doesn't work, post the command you're using here, and I'll take a look.