I also get a massage saying "Media Center 23 is running, but there may be a problem Possible causes:
1. The program is also running under a different user account.
2. Media Center 23 and Media Server are both in Windows start up. You must remove one.
3. The program is not responding for an unknown reason. Please reboot your computer. Verify that no other user accounts are running the program"
If you get that message it just means that some part of MC is still running when you tried to start MC again. So something went wrong and MC got stuck.
It usually isn't worth trying to work out what went wrong. It is a pretty rare issue unless there is a real Windows setup problem, or you are doing something unusual in your workflow.
Just reboot the PC and start again. If this happens a lot though, you need to ask for help in fixing it.
If your trial has now expired so you can't test anymore, I would be confident your issues can be solved and MC will do what you want, as long as you have the PC/Windows skills to recognise and fix them.
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Now;
1. The media files on the memory card will not be converted from 32bit to 64bit. They stay the same for both versions. Only the Media Center software is 32 or 64 bit.
2. Use the 32bit version of MC as it will work with Handheld sync, and should recognise a Pono connected to your PC. For simplicity, use the 32bit version of Media Center.
3. Do I understand correctly that the only copy of your audio files that you have are on the memory card? Or do you have them on another drive, or can you download them again from the original source?
As tij suggested, you need to copy them from that memory card to a safe place on your new PC before you do anything else. It doesn't sound good that your new PC doesn't recognise the memory card when it is inserted into the PC. It should see the memory card and allow you to copy the files from the card to your PC using Windows Explorer. Do not purge your Pono device. If the memory card can't be read directly, but the audio files can be seen when you plug the Pono into your PC (by USB I assume, as I am not a Pono user), then do that and copy the files to your PC that way. Keep these files as a safe backup. Do not include these files in any MC import process. If you can, make a backup of them on a separate hard disk, or another memory card. You can never have too many backups.
4. You have lost you MC library by the sound of it. If you had the old MC set to store tags in your audio files then you should get a lot of information back when you import those audio files into a new copy of MC, with a new library. You probably won't get all information back. For example, if you had custom Views in MC, they are lost. If you didn't store Cover Art in the audio files, then they are also lost, but can be downloaded again easily enough. But if you are just using MC as provided with all the default views and so on, and then transferring audio files to the Pono for playback, that can all be done.
5. When you get a new version of MC running, and it starts up, don't let it import everything it finds. You will see a countdown in the Action Window at bottom left when you first start a new installation. Stop that countdown. Then create a second copy on your PC of the audio files you saved in step 3. above. Put them in a Place where the new MC installation can see them, then import the files into MC. So in something like C:\Music\ or D:\Music\ or similar, depending on how your new PC is set up. Once the import is finished you should have all your music working in an installation of MC23. Check that all that works and fix any issues you see.
Once you get that far, if you decide to go ahead, come back and ask for more help if you need it.
Note: If you don't want to upgrade to MC23, you could just download a copy of the old version you were using and restore your old licence to that. Search the Wiki for "Restoring a License" to find out how. Assuming that you were using a copy of MC before and not a Pono specific piece of software. I can't remember for sure if Pono had a custom piece of software or always used a version of MC. Anyway, if your software was from a couple of years ago it was probably MC21. You can download the last version of MC21 from here:
https://yabb.jriver.com/interact/index.php/topic,105609.0.html