Connect both power and usb

I have got an old arduino uno r2 board. i need to connect the usb to the board and send input to the board through a php page. but the board not powered up using only the us cabe.
So can i connect both the power adaptor and the usb cable>???
Help me plsss/// !!

Yes, it is designed to auto-switch power.

But there given a jumper to switch between the usb and the power input
what to do about that jumper?
where to place it?

A jumper where? See attached Uno Rev 2 schematic

arduino-uno-rev2-schematic.pdf (91.6 KB)