Not receiving any emails (contact us or notifications)

Thanks so much orieszkowicz - that worked for me 100% i can now send and receive mails/notification including html!!!!

Thankyou BlizeH too - your solution gave me the first ray of light after about 5 hours of attempting to make this work...The plain text workaround worked for the contact form and order notifcations...however the mails I sent from the admin section were arriving blank.

This problem drove me crazy - I have encountered hiccups setting up mail on different systems before but this was ridiculous

I am using v 1.5.4

Doesn't work for me and I have 1.5.5.1. When I attempted to send it, the error logs displayed this:
2014-01-03 16:34:15 - PHP Warning: mysqli_fetch_assoc() expects parameter 1 to be mysqli_result, boolean given in /.../libraries/joomla/database/database/mysqli.php on line 483
2014-01-03 16:34:15 - PHP Warning: mysqli_free_result() expects parameter 1 to be mysqli_result, boolean given in /.../libraries/joomla/database/database/mysqli.php on line 512
2014-01-03 16:34:15 - PHP Warning: mysqli_fetch_assoc() expects parameter 1 to be mysqli_result, boolean given in /.../libraries/joomla/database/database/mysqli.php on line 483
2014-01-03 16:34:15 - PHP Warning: mysqli_free_result() expects parameter 1 to be mysqli_result, boolean given in /.../libraries/joomla/database/database/mysqli.php on line 512

Not sure if this says anything.

I need help on my opencart 1.5.5.1.
the problem is i don't get any message/error confirming that the email has been sent successfully or not when i sent an email to customer using sales/contact. Just nothing happen.
Please help