First thing, check to make sure Data is enabled
Freaked out a few times myself when I saw the radio/tower icon instead of the arrows. If thats fine, go back into PPST (##778#) and see which Mobile Profile you're using...switch to another, soft-reset, switch back to normal. If all else fails, you may need a DMU reset (highly doubt it). Also try activating another data phone and activating the TP again, has fixed quite a few Diamond/TP's.