Iphone 4 won't turn on? Even after holding power/home buttons?

This dumb phone is on the fritz. Essentially, it's my old cellphone. I'm using it because (GOOD TIMES) I dropped my other phone. Anyway, this one won't turn on. And yes, it's charged. I've had it plugged in all day and it was working earlier; however, it randomly kept shutting off. At one point, it would only turn on when plugged into my computer. Now it's officially off and won't turn back on. I'm getting my new phone this week, but until then this will have to do. Any ideas on how to jolt this thing back to life? I tried holding everything down and connecting it to the computer. Any other hints?

I had the same thing that your talking about to my girlfriends iphone 4. Did I drop in water, cuz it won't turn off. If you can't think of a reason why it is doing this, then what I did was held the power button at the top for a long time (like 20-30 seconds)
If that doesn't work then try holding the home and power button at the same time for 20-30 seconds. If that doesn't work then just hold the home button for the same amount of time. If all these methods fail, I think It might be time to get a new phone. I would also take it into apple and maybe they can run some tests on it

Bricked