Does anything happen you try to slide or tap the slider e.g. does it get a box around ? If nothing happens then try a soft-reset : press and hold both the sleep and home buttons for about 10 to 15 seconds (ignore the red slider), after which the Apple logo should appear - you won't lose any content, it's the iPad equivalent of a reboot.
If it gets a box around and a voice says what you've tapped then you have VoiceOver (one of the accessibility features) 'on'. Try triple-clicking the home button and see if that turns it off, and if it does you can then change what a triple-click does via Settings > General > Accessibility > Triple-Click Home. If that doesn't turn it off then you can either turn it off directly on the iPad (you need to use a tap-to-select and then double-tap to activate/type process and 3 fingered scrolling) to go into Settings > General > Accessibility and turn VoiceOver 'off', or you can do it by connecting to your computer's iTunes : http://support.apple.com/kb/HT4064