HI,
You may be using an application that disables the Home button without realizing it. Restart your iPad, open a different app and see if that makes a difference.
If the problem persists, try resetting the iPad. Press and hold the Sleep/Wake button and the Home button at the same time for at least ten seconds or until the Apple logo appears.
I've had this happen myself and restarting and / or resetting did the trick. Hope it works for you.
If not, check out the troubleshooting chapter in the iPad Online User Guide
here.
Carolyn 🙂