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$ ssh mykey.pem ubuntu@10.128.2.7 -v
OpenSSH_7.3p1, OpenSSL 1.0.2j 26 Sep 2016
debug1: Reading configuration data /c/Users/works/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Connecting to 10.128.2.7 [10.128.2.7] port 22.
debug1: Connection established.
debug1: key_load_public: No such file or directory
debug1: identity file /c/Users/works/Documents/interface setup/ifx_key.pem type -1
debug1: key_load_public: No such file or directory
debug1: identity file /c/Users/works/Documents/interface setup/ifx_key.pem-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.3
debug1: Remote protocol version 2.0, remote software version OpenSSH_6.6.1p1 Ubuntu-2ubuntu2.8
debug1: match: OpenSSH_6.6.1p1 Ubuntu-2ubuntu2.8 pat OpenSSH_6.6.1* compat 0x04000000
debug1: Authenticating to 10.128.2.7:22 as 'ubuntu'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: curve25519-sha256@libssh.org
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
debug1: kex: client->server cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:R+d2ELtCJyoeyHMfivCsGKk98GOIfxxsTEPAFmKkSOI
debug1: Host '10.128.2.7' is known and matches the ECDSA host key.
debug1: Found key in /c/Users/works/.ssh/known_hosts:1
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey
debug1: Next authentication method: publickey
debug1: Trying private key: /c/Users/works/Documents/interface setup/ifx_key.pem
debug1: Authentications that can continue: publickey
debug1: No more authentication methods to try.
Permission denied (publickey).

I used to be able to ssh into this machine until yesterday.
Is there a way to login into it?

Only if you have a private key that is reference to in the .ssh/authorized_keys on the server. Have you deleted that file or altered its contents?

If you deleted the information, you won't be available to log into the server again, if you don't have physical access to the disk.

This is basic ssh security, if you don't have the appropriate key which is mentioned in the .ssh/authorized_keys, you don't get access. That way you make sure that noone else can easily access your server.

$ ssh mykey.pem ubuntu@10.128.2.7 -v
...
debug1: key_load_public: No such file or directory
debug1: identity file /c/Users/works/Documents/interface setup/ifx_key.pem type -1
debug1: key_load_public: No such file or directory
debug1: identity file /c/Users/works/Documents/interface setup/ifx_key.pem-cert type -1
...
debug1: Next authentication method: publickey
debug1: Trying private key: /c/Users/works/Documents/interface setup/ifx_key.pem
debug1: Authentications that can continue: publickey

The only key which your client tried to use is ifx_key.pem. It looks like that file isn't actually present (the "type -1" line). If that's the key which ssh is supposed to authenticate with, make sure the file is actually present on your local system and that you have permission to read it.

$ ssh mykey.pem ubuntu@10.128.2.7 -v

This suggests that you want ssh to use a different key file named mykey.pem, but you didn't specify the command correctly. To specify a key on the command line, use the -i option:

$ ssh -i mykey.pem ubuntu@10.128.2.7 -v