Power button Powers off but doesn't sleep
hi, I have an iPad 3 16gb on IOS 8.4 and It doesn't let me put my iPad to sleep, I press the power button and it does nothing but if I hold it down it brings up the power slider and if I press the power button and home button and it takes screenshots but doesnt put the iPad to sleep, I turned assistive touch on to try and use that to put my iPad to sleep and the sleep button doesn't work either! It is annoying me a lot and I don't understand we its happening, I tried restoring it and it still did nothing I need help to fix this issue, if anyone knows how to fix this it would be greatly appreciated
thanks
iPad, iOS 8.4, Ipad 3 need help urgently