1st of all, Welcome    a real female user ?? Will add u to front page owner list 
So your phone new open box? Well, try take out the battery .. rest a while.

Reinsert and try power on.

If still no luck, off it and let it charge until tomorrow morning.
Now, here is the point .. if next day morning still no luck then you better return to the shop for exchange 

just wanna check, you bought AP set or original set? from where?

haha , my wife also real female Defy user 

and my wife's Defy got restart problem when we just get the phone, but lucky I test enough at the shop. Then we have to come back 2 days later for another new set. ( Sunday shop close )

btw, My own set is Original SG set ( direct delivery by my brother in law  ) then my wife unit is AP set France unit.