Hi and welcome to the forums!
This is typically a sign that your phone does not have sufficient charge to turn on. Plug it in to the wall using the OEM (BlackBerry) charger and let it charge for a couple of hours. The phone should turn on just fine afterwards.
Note that because of the charge level, using a car charger, USB cable or a non-OEM charger may not work. When we've seen this problem before, it's usually only helped to charge using the actual wall charger.
In addition, you should also be aware that the phone will not turn back on until it has charged sufficiently. Usually a half hour to an hour should be enough charge to turn the phone on, but I'd recommend charging it for 2 hours minimum, and then charge it fully tonight.
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