Quote Originally Posted by Merciless View Post
When my phone's hooked up on my PC with the USB cable, the screen always stays black, it just "flashes" for a second and stays black (by holding the sleep/wake button & home button at the same time for 30+ seconds)

However, when it's being charged normally, that's when the apple logo appears.

So I can't really go into recovery mode
I know absolutly nothing about iPhone hardware

I'd say something is wrong with the battery or the battery install. It makes sense that the screen will flash for a second without USB (barely any power in the battery) and with the USB, it'll start to boot, but then it switches to the battery to charge, and you crash..

Just a guess