Hello James! This TinyUmbrella error is one of the most common issues jailbreakers face, so don't worry, we have just the right solution for you, as we have had this message as well in the past.
As a first solution: make sure you have downloaded and installed the latest Java version. We suggest though, to download and install both the 32-bit and 64-bit Java version on your PC. As soon as you are done with the above step, try to launch TinyUmbrella again and see if you get any TinyUmbrella error messages.
If you have downloaded the latest Java version, but you are seeing the above issue, here is a second option of what you need to do fix the "No JVM could be found" TinyUmbrella error. Find and delete javaw.exe, java.exe and jawaws.exe files from your computer (you'll see the exe extension only if you have enabled the "show extensions" option). You'll find the files in the "C: > Windows > system32" directory.
Once you throw these files in the trash, try to reinstall your Java, keeping in mind that you need the latest version and both 32-bit and 64-bit versions to get rid of the TinyUmbrella error.
In some instances, you may still get the same TinyUmbrella error. If so, a third option we recommend is to obtain the path to the Java runtime folder on your computer. A search for java.exe could ease this process.
As the next step to eliminate the TinyUmbrella error you'll need navigate to "My Computer > Properties > Advanced System Settings and choose Environment Variables". In the pop-up window, search for "System Variables" and choose "New". Name the new variable to "EXE4J_JAVA_HOME" and note that the value is the path you got when searched for the java.exe file. When prompted, click OK twice to leave the dialog box. Now you can try to run TinyUmbrella.
That's it. Any of the above three solutions eliminated the "No JVM could be found" TinyUmbrella error.
Hope this will work out for you as well!