The first question is whether, when you upgraded to version 4.36, did you save the program itself, not just install it? If you saved the program, all you need to do is copy it from the old pc to some medium like a flash drive, and then copy the program from the flash drive to your new pc, and then run (install) it, and you're fine. If you did not save the program, I suspect you'll have to purchase the new Pro version 5.40, and this time, SAVE the program and then install it. The privacy regulations that doctors adhere to usually means their audio files have codings that are outside of ExpressScribe's free version, which is pretty limited.
Like you, I've been using Scribe for 15 or so years, and I learned the hard way, to always save programs older than the newest version being issued in case the latest has bugs or problems that make it necessary to reinstall the previous version. Since they always have the same name, you want to save it as something unique, such as the date and version number.
If you do have to purchase this latest version, make sure you also save your documentation, invoice #, activation code, license, and key. This is the proverbial ounce of prevention... take two and call me in the morning.
KRN