So frustrated with bedtime

I am at my wits' end with Kate and bedtime. I put lights out at 7:20 pm - a little earlier than usual b/c she seemed tired - and here we are at 8 pm and she is still awake and getting up and down out of bed. NOTHING works on this child. I took away her favorite toy, 3 ponies, and her bicycle privileges tomorrow. She doesn't care! I even spanked her butt - something I swore I would never do. She doesn't like it but it didn't keep her in bed. She got right back up. Todd is now sitting in her room to make sure she doesn't get up and he will have to stay until she falls asleep. She was up at 6 am this morning and yesterday morning too. She should be plenty tired. I just want to scream!!!!! And, now with this Jack in the bed syndrome tonight she will either be up in the middle of the night and/or up at 5:15 am tomorrow. I can't live like this! I swear I've tried all the 'solutions' in all the books I've read. Nothing is working. I did everything right, right from the beginning. She was always on a schedule, naps and all. She slept straight thru the night from 9 months on and was a fabulous sleeper until the last 6 months or so. The books said follow a routine - same all the time, teach them to put themselves to sleep, etc. - I did all that. What is wrong?