Do this you will get back your Marinecoin in new windows computer:
Install and run Marinecoin first, no need to sync fully, just sync for couple of minutes first.
Go to your folder at windows
C:\Users\YourUsername\AppData\Roaming\MarineCoin
Under this folder, you should see a file "wallet.dat". Delete this file. Then rename your backed up file to this name, copy and paste into this folder.
Then restart your Marinecoin, and fully sync to end. Your old MTC should be back in your wallet.