cannot turn on ipad, icloud backup message

I have not been using Icloud back up because it says it is at capacity, which is fine. However now on my ipad there is a message "This ipad hasn't been backed up in 21 weeks. Backups happen when this iPad is plugged in, locked, and connected to the Wi-Fi. When I press the OK button or Slide to Unlock, the iPad is "locked". When I power off, it powers off, comes back on, but I still cannot use the OK button or Slide to Unlock. I did connect the iPad to my itunes account and backed it up to my computer. How can I get my iPad to get rid of the iCloud message - how can I deactivate iCloud?
Thanks