Version of InDesign? OS?
Is there an object selected? Have you tried clicking the little arrow to the right of the box to open the tint slider?
I don't seem to be able to type the tint values directly, either, in versions of ID from CS6 forward, but I'm not sure if this is normal or a sign of damaged prefs, so if anyone else would like to check, that would be great. The slider works fine.
Win7, x64, CS6.
No problems with direct entering tint values here.
Except [Paper], of course...