installation os x on Mac pro 2 from scratch I purchased mac pro 2 model no# a1186 few days ago with a new Hard drive . Now im trying to install os x from usb.
i made bootable usb through another mac mini machine  by formatting it through disk utility and transfer dmg OS X lion 10.7 in it.

Now issue is that i cant boot from usb and the Hd is new, nothing in it so how to boot usb on mac pro 2. 
I have tried key such as cmd (alt) + R  key but nothing happening. Its just shows grey screen and after few seconds question mark symbol blinking.
And when press and hold "R" key . it just shows a mouse cursor on screen and nothing else.
Please guide me how to install OS x in it. Im in urgent.

PS : am i making any mistake during making bootable usb or whats the key combination for booting mac pro 2 to usb?
To make a USB installer from the 10.7 .DMG you need to open the .DMG, then open the installer application by right-clicking and selecting Show Package Contents and then find the actual installer itself, InstallESD.DMG.

Use the Restore function in Disk Utility to copy InstallESD.DMG to your USB device (if you receive any errors, try mounting InstallESD.DMG first before copying it). You should then be able to boot your Pro from it :)