How to fix unexpected server closed connetion in putty

Question

Hello please help me friends, I am trying to login to server through ssh with putty. But after setting up the hostname and putty is ready, it will allow me to type the cpanel username. But after sometimes, it shows a message box (unexpected server closed connetion). Please is it network problem? Because there is something I don't understand about this problem.I need suggestions. Thanks. This is my sshd_config I have tried that @Nic but not working... This is my sshd_config

#$OpenBSD: sshd_config,v 1.65 2003/08/28 12:54:34 markus Exp $

# This is the sshd server system-wide configuration file. See # sshd_config(5) for more information.

# This sshd was compiled with PATH=/usr/bin:/bin:/usr/sbin:/sbin

# The strategy used for options in the default sshd_config shipped with # OpenSSH is to specify options with their default value where # possible, but leave them commented. Uncommented options change a # default value.

#Port 22

#Protocol 2,1

Protocol 2

#ListenAddress 0.0.0.0

#ListenAddress ::

# HostKey for protocol version 1

#HostKey /etc/ssh/ssh_host_key

# HostKeys for protocol version 2

#HostKey /etc/ssh/ssh_host_rsa_key

#HostKey /etc/ssh/ssh_host_dsa_key

# Lifetime and size of ephemeral version 1 server key

#KeyRegenerationInterval 1h

#ServerKeyBits 768

# Logging

#obsoletes QuietMode and FascistLogging

#SyslogFacility AUTH

#LogLevel INFO

# Authentication:

#LoginGraceTime 2m

PermitRootLogin yes

# The following setting overrides permission checks on host key files

# and directories. For security reasons set this to "yes" when running

# NT/W2K, NTFS and CYGWIN=ntsec.

StrictModes yes

RSAAuthentication no

#PubkeyAuthentication yes

#AuthorizedKeysFile .ssh/authorized_keys

# For this to work you will also need host keys in /etc/ssh/ssh_known_hosts

#RhostsRSAAuthentication no

# similar for protocol version 2

#HostbasedAuthentication no

# Change to yes if you don't trust ~/.ssh/known_hosts for

# RhostsRSAAuthentication and HostbasedAuthentication

IgnoreUserKnownHosts yes

# Don't read the user's ~/.rhosts and ~/.shosts files

#IgnoreRhosts yes

# To disable tunneled clear text passwords, change to no here!

PasswordAuthentication yes

#PermitEmptyPasswords no

# Change to no to disable s/key passwords

#ChallengeResponseAuthentication yes

# Kerberos options

#KerberosAuthentication no

#KerberosOrLocalPasswd yes

#KerberosTicketCleanup yes

# GSSAPI options

#GSSAPIAuthentication no

#GSSAPICleanupCreds yes

# Set this to 'yes' to enable PAM authentication (via challenge-response)

# and session processing. Depending on your PAM configuration, this may

# bypass the setting of 'PasswordAuthentication'

#UsePAM yes

#AllowTcpForwarding yes

#GatewayPorts no

#X11Forwarding no

#X11DisplayOffset 10

#X11UseLocalhost yes

#PrintMotd yes

#PrintLastLog yes

#KeepAlive yes

#UseLogin no

UsePrivilegeSeparation no

#PermitUserEnvironment no

#Compression yes

#ClientAliveInterval 0

#ClientAliveCountMax 3

#UseDNS yes

#PidFile /var/run/sshd.pid

MaxStartups 10:30:60

# default banner path

Banner /etc/banner.txt

# override default of no subsystems

Subsystem sftp /usr/sbin/sftp-server

Answer 1

Head to your putty settings -> Connection and set the value of 'Seconds between keepalives' to a value like '30' and retry.

If that doesn't work try show us the contents of your sshd_config

cat /etc/ssh/sshd_config

Edit: Add this to your sshd_config

# Enable TCPKeepAlive
TCPKeepAlive yes

Good Luck!