Php script - need to improve caching mechanism and optimizing mysql queries.Getting internal server 500 error due to heavy load - repost 2

Hello, i have a php video script(custom written) on my web site,including legal adult [login to view URL] has heavy loading issue. When online users excess number of 1k, apache server giving internal server 500 [login to view URL] is a caching system on script but i m not able to check or develop it to work correctly.I think the main problem is too much database queries occurs at the same [login to view URL] is hosting on Hostgator's web hosting service. When i ask my website hosting provider(which is hostgator) they said that process limit has been exceed(which is limited to 25 processes).Database queries takes too long so need to implement table indexing and query caching or something else to decrease process [login to view URL] to VPS or Dedicated Server is not an option for now. I need a php developer and mysql expert to solve this issue.I can give detail informations who want to work on thid project