Here we go again. The linux basics are completely missing, but you think it's a good idea to just rent a server that's open to the internet.
Sorry, not to pick on you, but why not just practise with a VM first?
Firstly, if you have a ppk key file, you've already done something wrong.
You need a private key and a .pub key.
Just follow these instructions:
https://phoenixnap.com/kb/generate-ssh-key-windows-10
then enter the .pub key on your server via SCP (look at fvbor's post)
and then simply try to connect via terminal:
ssh -i c:\user\...\your private key (not the .pub) root@IPADRESS
and ps:
are you sure that the password did not work? Linux has no ECHO for the password (so the cursor does not move. No *****)