power on issues while connecting external supply

[hariharan_srm]

HI i am using nordic nrf52840 dk(pca10056) . i am using ble_app_uart example code for my development. i have connected usb in j2 but when i keep my power switch in usb adv led is not blink while keeping only on vdd with j2 on usb supply the ble is advertsing  why?. i want to know how to give external power supply to the board what are the procedures needed to be done whether any jumper switching or any soldering should be done . and how much volatge should be given to external power supply to the board. and then when i connect the nrf52840 tx pin with my lpc controller my lpc controller rx io getting low whether it nordic has been pulling low the io(rxpin) of my controller  

[hariharan_srm]

i have connected usb type(b) to j3 and kept the switch to usb but no advertsing happens and i have also connected external supply 3v to p21 the board is not on . only while connecting usb with j2 and keeping the switch on the vdd mode board works . whetherany jumper has be connected or any solderings to be made between any things. i have also kept the nrf only to default siwtch in both ways but no board powersup. i wan to step by step procedure to connect the external supply to p21 i have connected the volateg and gnd to p21 but no boot happening