Im using arduino mega pro mini board. it seems like most of the pin numbers onboard correlate to the pins in arduino ide.
pins so far pins 24,25,26,27,28,29,30,31 have not worked as input for me. are there any specific pins i cannot use as input?
What board entry did you use when you burned the bootloader ?
programmer is set to Arduino ISPi dont think i have messed with the bootloader. how can i find out?
Does/did the arduino mega pro mini board have the bootloader installed for you ?
it must have. i dont think i ever touched the bootloader. i took it out of the box and started using it. i can tell you that it takes a few seconds for the arduino to boot
when i set pin 31 to output it works high/low. it wont work as input. it looks like lots of them dont work as input. pins 14,15,16,17 are working as input for my buttons
When you upload a sketch, what do you select as the board ?
the board selected says "Arduino Mega Or Mega 2560"
Under "Arduino Pro or Pro mini" it only give cpu options for 328p and 168. my board says Mega 2560 Pro Mini V1
Maybe look at the pins_arduino.h file (i think under hardware) and see if something stands out.
There are lots of ground terminals on the board. apparently they are not all connected together. on the usb header side there are grounds on each side of the board. they are not connected together
There seems to be some doubt as to just what board this is.
Please give a Web link to it.
On an ATmega2560, all of the IO pins should be usable as inputs.
It is most likely that the pins are not where you think they are. Since "arduino mega pro mini" is not an official Arduino board, it doesn't have an official pinout, and it would not surprise me if different vendors were selling boards with the same name, but different pinouts 
Possibly you have a bogus unit Or a cheap copy coming from the 25th hour batch trash can…
It Would not be the first time crappy units are getting into the market from careless sellers
Is this the board?
https://robotdyn.com/mega-2560-pro-mini-atmega2560-16au.html
If so click on the documents tab and then to pin out to get the pin out you need.
All pins should be capable of output. If not ask the vendor about it.
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