hi lexortiz and welcome to the syschat forums
i did a quick search for the model of motherboard: ASUSTeK Computer Inc. - Motherboards - ASUS P5G41-M LX
on that link, click the CPU Support List button
The list of supported CPU's do not include your Pentium 4 processor.
i believe this is the link for your processor: IntelÂ® PentiumÂ® 4 Processor 620 supporting HT Technology (2M Cache, 2.80 GHz, 800 MHz FSB)with SPEC Code(s)SL8AB
while the ASUS website does not specifically include your processor model, they are both socket 775 technology. my suggestion is that you bring your processor and fan to them, and have them test of it fits and actually boots the motherboard.
this way you test both your old processor and the new motherboard