Try this;
Do a power supply reset by unplugging the power cord, then push the power button in and hold for 10 seconds. Re-plug the power cord, and try to power on the computer.
Lets see if the Asus site allows links to their troubleshooting section.
Trobleshooting MatrixThere is an error on their link to the section on led lit-->no display-->fan spinning-->no abnormal beep sound.....
The link for your situation is the row above, as if you had abnormal beep sounds. But, of course, you have no system speaker attached, so read both.
If this fails;
Do you have a PS/2 keyboard to try?
...and you are sure that the processor is supported?
Athlon 64 X2 6000+ (CZ),2MB,rev.F3,125W,SocketAM2 is supported for the motherboard. Note the CZ version of the chip. Is this what you have?
The problem here is that in the absence of beep codes (which may be helpful) we are taking shots in the dark.