even manually?
have you tried to restart the phone?
maybe a *228 option 1+2 (can't hurt to try that)
also, go to settings, accounts, click on your gmail account and make sure the sync is selected.
and if you have the power bar widget (if not, you can add it, i'm not sure how else to get to the apn option) make sure the sync icon isn't deselected.
finally, in settings, battery, make sure your profile isn't on some weird super saver profile, as that will cut the data connection off rather quickly.
if none of those work, i'd try a factory reset