Server hacked?

[redblue]

Hello,

I have been experiencing a few problems simultaneously on my server and I am not sure if it's because someone has hacked into it. The following are some of the problems:
1) Unable to login via SSH to the server
2) Unable to receive mail from the server (this is unusual because I get tons of spam mails every day and my spam filter haven't even been getting any spam mails for the last few days)
3) Test e-mails sent from my Hotmail account never arrive to the mail account served by the server
4) Any attempts to add/remove/change password on the mail accounts on Plesk results in an error. For example, if I try to create a new mail account I get the following:

ERROR

Unable to create MailManager object: mailmng failed: Empty error message from utility.

--------------------------------------------------------------------------------

0: /usr/local/psa/admin/plib/class.MailManager.php:52 psaerror(string "Unable to create MailManager object: mailmng failed: Empty error message from utility.")
1: /usr/local/psa/admin/plib/cmd_mail.php3:1367 mailmanagermaker()
2: /usr/local/psa/admin/htdocs/domains/mail/mail_name_preferences.php:122 mn_new(integer "2", string "test")

Can someone please tell me what I need to do?