Why I Am Insane

They say the definition of insanity is "doing the same thing over and over, expecting different results."  Well then by all means I am INSANE.  Although we all knew this.  I have decided that this whole being a mom thing is just not something that I am good at.  I know it's a little late after 5 kids but I give up.  I sit at a nail table in my living room all day and work and work so that we will have the money to support these children and they don't care.  They just don't care.  I put them in the best schools so that they have the opportunity to have more than I do and they don't care.  I buy them nice things and they destroy them because they just don't care.  Somewhere along the way they learned not to care and I didn't think that I was the kind of mother to teach them that.
I am to the point where I give up.  They do what they want when they want, they talk to me with total disrespect and they know that because I'm behind the nail table with a client that there is nothing I can do.  I am so tired of friends and their "if I had talked to my parents that way..." comments.  What am I supposed to do?  It has become nearly impossible to discipline our children anymore.  If we spank we get turned in for child abuse and I'm sorry but grounding them or taking things away does nothing.  I was better at this at one point.  I had it down when there was only three of them.  I knew what to do and how to get things done when I wasn't a working mom but now that I have to work they seem to have lost all respect for me.  It's like they don't care about me or my existence.  I am ready to walk out for a while and see if it would make a bit of difference to them.
I would be lying if I said that I don't care about them anymore.  It breaks my heart everyday.  I spend so much of my time worrying and crying because they don't seem to care.  It hurts so much.  I don't know what to do to fix this.  I just seem to be "doing the same thing over and over expecting different results."  And that is why I am INSANE.