Gen 1 iPad has black screen and more.

I have a 1st gen ipad. Screen is black, when charger is plugged in it will flash for a split second every few seconds but no computers or even itunes will recognise it's even plugged in. The 2 button technique does nothing regardless how many attempts are made both plugged in and unplugged. I replaced the charging port, and the battery tests that it does function. Also, iMyFone Fixppo doesn't work, but it does seem to recognise the device enough to tell what gen it's from and the OS installed. Any ideas?