Clean up the code in www.hrinvasion.com

Clean up the code and eradicate all the little errors please! I have had a website built [login to view URL] (built using Joomla) but I keep getting error messages saying "Loaded but with errors on page" and "messy code". I'm not 100% what the problems are but would like someone that will know to fix my new site and get it working 100%. I have tried using explorer and firefox but still have problems in the admin section altering and updating the content. Please feel free to message me for anymore information. Happy Bidding