Exact the same issue here, and seeing other posts on this forum, we are not the only one... Shop where I bought the phone YESTERDAY (in Holland), does not wan to replace it or return my money, guy just wants to repair it? OK, that's a dodgy side of the shop, but I believe that HTC should do something about this. I think that since yesterday, I have sent about 30 'Abnormal reset' reports. The phone prompted me to send this to HTC and I did.
I hope that you can resolve your issue. Maybe an idea - I have Lebara prepaid card - and it happens every 2 minutes that the phone resets itself. Maybe if you try another card - you might get better luck - but that should not be the point - we just want to use our own sim-cards, right?
If you manage to get the solution - please let me know. Cheers and good luck!!!!