Just to be unambiguous, you have tried the reset button (paperclip through the pinhole in the back). I think that's what you meant, just wanted to be sure.

When all else fails, try this: Take the batteries out, and with them out, carefully connect the terminals in the battery compartment together with something metallic (like a paperclip). Leave it for a few minutes, then put the batteries back in.

I know that sounds bizarre, but the Pronto draws so little current that you have to discharge the capacitance of the device itself to really make sure nothing is powered...

The only time that the reset button hasn't worked for me, this technique did the trick.

Aside from that, the 'reset' button is a real, honest-to-goodness reset. If it's having no beneficial effect, either a) the reset switch isn't working, or b) the OS in flash somehow got corrupted. Either way, if things are that bad, there's not much that can be done except to exchange the unit, I'm afraid.