can't even access the runway
What do you mean? The program doesn't start or it starts with an error (if so, could you please give me the error message)?
If you want to keep your previous data it's just a matter of replacing the new 'Data' folder inside your new mGalaxy installation folder with the 'old' one!
1. Install mGalaxy in a new location (don't un-install or remove the previous one now...we need it)
2. Copy/Paste (or drag-and-drop) the 'old' 'Data' folder that you'll find inside the 'old' mGalaxy installation folder into the 'new' mGalaxy installation folder.
3. When asked for, choose to 'Replace' data
Please, tell me if that fix your problem!!