Psu and ramps issues

Hello everyone. So i finally got a arduino mega and ramps 1.4 for my custom 3d printer.both r from china just saying.so here is the thing i connect mega with the usb from computer and i connect the power from a psu (10A,340W) on the ramps.psu wroks fine but if i connect both inputs on ramps the psu doesnt work ( can see the psu fan not moving). If i connect the psu on heatbed input only it works but if i connect the psu to the normal input psu doesnt work.both leds on mega and ramps r working so i guess they both work but cant understand what is causing my psu not working. Any hints and how to fix this??

thereisajumperrightnexttotheresetbuttononrampsboard.howisitjumpered?

Sorry, it seems my space bar is partially broken

Thx for replying but.more info would be appreciated.there r some pins near reset but there isnt any jumper.should there be a jumper and if so in which pins? If possible apic would be better for understanding. And sry to hear about ur space bar .