1) you not pushing in or holding the power button long enough
2) Your battery is shot.
3) your phone is not holding a charge or charging the battery.
Because even with a bad rom you will atleast see the M (now I may sound like I am about to contradict myself from my previous post but let my clarify). The problem with your phone is not the rom but either the battery or the phone. If you put your battery in another droid and it come on easily then you have a bigger problem. A charged battery will turn your phonr on. Now the question is how are you charging it. Are you charging it in the bad phone or are you using another device. I would try charging it in another droid to get a full charge then put it back in.
I just said the battery is the problem why am I screaming sbf. If you know it has nothing to do with the rom and you know your phone is not the problem then dont bother. If you suspect you may have a bad phone you do not want to return a rooted droid back to verzion. And that is why I am hollering sbf asap once you get a strong battery.