since you didn't mention OS or what you have or have not attempted so far other than reading "All of the other threads are bits and pieces and I have been unsuccessful" would be to follow this link to a forum that will look over a HijackThis log you will need to create.
When arriving at the link please take the time to read their requirements for posting the log.
I have had my desktop hijacked. It now displays the smart security ad. I am computer illiterate. Can someone please post the cure for this in one post. There are several disjointed threads about this that talk about Hijack program scan etc. I don't know what that is etc. I can go into the registry and delete stuff, but I need someone to please give me complete directions. All of the other threads are bits and pieces and I have been unsuccessful.