Take a look here: http://www.elhvb.com/mboards/OEM/HP/
Your board was used on these hp models:
Echo GL Asus P4G533-LA/P4G533-GL (10/16/2003-I845G/ICH4/IT8708-P4G533LA ) : 354n (US/CAN), 525w, 533w (serno MX IT8708F), a210n, a206x, a345w, a336n, a335w, a328d, a320d, a318d, a316n, a312d, a307i, a305wm, a305w, a305i, a300n, a424x, a422n, a412n
Do you get as far as the bios string at boot? That should help you narrow things down. Also, have you tried resetting the cmos? If you can't find the jumper, simply remove the battery for a few minutes.