Removing transistor Q21 worked for me!
I had the exact same problem with my Compaq Presario S5000SX with ASUS motherboard P4G533 (Echo), S/N MXK33... and the solution above fixed it!
The wrong end of a USB camera cable was pushed into the front panel USB port, and the computer froze. Rebooting produced the initial boot splash screen (which says press F1 or F10 for BIOS Setup or Recovery), a beep, followed by a continuous beep. Pressing keys produced no change. Booting without keyboard/mouse produced same result.
Based on the solution above, sounds like the Q21 transistor shorted out, causing the motherboard to not boot. I pulled the Q21 transistor off the motherboard (using an xacto knife to cut and small needle nose pliers to pull), and was able to boot! Hooray!
The link below shows pictures of the motherboard. The Q21 transistor is just above the USB1 (Front USB) port at the bottom of the case.
http://h10025.www1.hp.com/ewfrf/wc/d...359576&lang=en
