By using this command you have created certificate request server.csr:
openssl req -nodes -newkey rsa:2048 -keyout myserver.key -out server.csr
To see the contents of the request you can use:
openssl req -noout -text -in server.csr
Then you have uploaded server.csr to namecheap and got your certificates.
If your private key (myserver.key) is empty then i think you somehow corrupted it. You can reissue you certificate with the new key and certificate request. Drop a line to namecheap support, i think they can resolve this situation.