Can't boot from usb to install maverick for iMac 2007 model 1225

I got iMac 2007 model and the DVD drive is not working. Recently the hard drive crashed and I have replaced with a new one.

I have created a bootable usb of Maverick to install the OS X. To test if the usb work, I tested with Mac book air and the machine can boot from this USB.

I plugged in to the iMac and hit option while power on, nothing happen, I could see grey screen only. >>so I swapped the hard drive back to the original one which has OS X on it and tested it again. I now can see an option of boot from hard drive but no usb showed up.

At this point, I guess I can be sured that the keyboard is working fine.

Any one could explain or guild me to install from USB to iMac 2007 model. I am also wondering if this iMac model support boot from USB. if not Can I use PC's DVD dive to hook up and install OS X.

Thanks