That's called Touch Flo 3D
Touch Flo 3D is HTC's user interface that comes with the Diamond.
It is probably disable on your phone and you can get it back up in "Settings":
Setting -> Today -> Items
Check "HTC Touch Flo" (you can uncheck everything else)
(restart the phone if no change happens)
There you go...
Now your next step is to look for a nice cooked ROM and get rid of that old stock ROM!
Device: Diamond (DIAM110)
HardSPL: 1.93 Olinex Unsigned Version
ROM: GEN.Y D2X R1 [WM6.1 B21054 w/ SENSE2.5 WWE]