Monitor turn off after stand-by

[Fun&Moog]

Hi everyone,
This is my 2nd post. I really need some advice with my PC which is driving me insane.
The problem is that after coming out of a stand-by, everything is normal for a few minutes, then the monitor turns off. Sometimes, the HD light stays on, sometimes not, but in all cases the on/off light is still on.

What I do then is I turn the PC off and on again but the problem doesn't occur again untill I do the stand-by again.

I suspected that Windows or my TrendMicro updates are triggering this, but now I don't think so.

Could you pleas etell me at least where to look for the culprit? Is it a sign of a much more serious problem?

Thanks in advance. My system specs are found below:

Brand/model: HP 734n
Motherboard: FIC AM37 socket A
Processor: AMD Athlon 2400+
RAM: 512 MB
Video Card: Nvidia GeForce4 MX420
onboard sound: Realtek AC97 (disabled)
Sound Card: M-audio audiophile 2496
System: WinXP version 5.1 with SP2

Thanx.

[Fun&Moog]

Just a follow up. I updated the Nvidia GeForce driver and the problem no longer exists.

[Fun&Moog]

Unfortunately, it came back a day or two later and once it did occur out of the blue while not coming out of a stand-by.
It's interesting that it gave me some error message about one of my startup programs, the MotherBoard Monitor. I disabled it, but don't know if it is the culprit or not.
Any ideas at this point will be much appreciated. Thanks.

[Fun&Moog]

Ok, the last time this occured I took notice of the time and took a look at the Event Viewer. There is an error that registered exactly at the time the problem occured. It is Event id 1002 from source Dhcp, and the error says:
"The IP address lease <ip address> for the Network Card with network address ###.###.###.2 has been denied by the DHCP server ###.###.###.1 (The DHCP Server sent a DHCPNACK message)."

Any idea what is going on here? Is there a problem? and how do I fix it?
Thanks.