Like many others have said..
Press & Hold - Turns it on (should be an intermitant blink)
This is Semi Auto with Eyes On.
(It wont fire without a ball in the breach)
Press it once - (It will do 2 quick blinks evers second or so)
This is still semi auto but eyes are now off.
(Handy for dry firing marker..)
Press & Hold - like turning it on, if you do this at any time
when it is on, it will turn off again.
The only way to put it on Ramping is to open the grip frame..
Theres a small button on the main board that you need to press to cycle through the options like BPS up, BPS down, Dwell Up, Dwell down, Fire mode up, Fire mode down. (if its a UK board it will only have 2 fire modes, Semi auto & Rebound (Ramping)
The Ion is capped at 10BPS on the ramping for some reason, it will go below that, but not above..
The programming is displayed by 2 coloured LED's on the board
(Do not attempt to reprogram it without the manual in front of you..) the on/off button cycles through the settings with whatever mode your in, when you got the settings where you want them, pull the trigger to save settings and return to normal.
Back to your problem..
change the battery, try turning the reg down and seeing if it fires, make sure its in Eyes Off mode (turn it on, press on/off button once so it blinks twice..)
NOTE:- if it still isnt firing, make sure you count how many turns back you turned it and be carefull not to turn it too far above what it was before you tinkered with it, it gets a little dodgy at around 170+ PSI.