How do I turn on an iPad (first revision) during it is loading. Or how do I turn it on at all?
When I plug it in, the display shows a battery symbol with a little bit of red juice on the left side (seems to be empty). Then the display turns off after a few seconds.
All iOS devices do that after they have been completely discharged.
If it does not boot up with in 5-10 minutes of being plugged in, then it could be an indication of hardware failure. The battery is likely not accepting a charge.
You are seeing the (very obvious) low-battery indicator. The battery does not have enough power to boot the device.
A first-generation iPad is at least 4 years old - if it has been used regularly the battery has likely done enough cycles that it needs to be replaced.
If it has been left on the shelf for extended periods the battery has discharged itself - this is very bad for lithium batteries.
And finally, you must use a high-capacity USB charger, the small cube for your phone will not charge an iPad, neither will a powered USB hub.
Assuming you have a suitable charger, leave it plugged in overnight. If it still won't start, you need to replace the battery (or the iPad).
