I am trying to connect a 2 Tb external Hard drive (ADATA HD710) to my raspberry pi, but the problem is that when I connect it to one of the USB ports, the raspberry pi stops working. I am not sure if this is for the current (I have a simple charger of 5V - 2000 mAmp), or maybe I have to do an overclock or something like that. I would appreciate any suggestions to solve this problem, I tried to look for the current specifications of my external hard drive but I couldn't find anything, thanks
It sounds like your RPi and the HDD is not getting enough power. Normally, a 2.5 inch HDD (like HD710) requires 5V 0.6A (or even up to 1A) (nom.) power to function properly, so you only got another 1A for your RPi 2, which still not count the headroom for your PSU (some bad quality PSU may not deliver 2A as the spec). If you connect other peripherals to your RPi via USB/GPIO, your available Amps will be lower. Most importantly, HDD requires spin up and we should also take the spin up current into account.
I suggest you to have your firmware switched to 1.2A USB power and use a powered USB hub to power the HDD, or use a Y-usb cable with a separate power supply (you can make one by yourself too).
However, I DO NOT SUGGEST you to overclock your RPi, as it made the RPi requires more power, and also introduce instability problem provided that your Pi already did not have enough power.