Monitor won't power on at startup

in the OLD days, AT power supplies has a port for the monitor to plug into so that when the computer turned on so did the monitor. Not so with ATX power supplies. If the on button on the monitor is OFF [assuming you've got the thing plugged into a surge protector and THAT is plugged into a wall socket] well, the monitor is off until you push the button on. Not sure if they make ATX power supplies with a port for the monitor. Best person to ask that is TheChas or go take a peak at some of the power supply maker's web sites [enermax,antec,thermaltake, sparkle [gods but they are terrible].

I think I'm missing your question so excuse me if mine seems dumb or obvious. Is the power button on the monitor being physically pushed when the PC is being turned off? If so it won't come on. Or are you saying you have to push the button even though it wasn't pushed?

This does sound a bit strange.

Correct me if I am wrong.
When you power up the PC, the monitor power indicator glows yellow, and stays yellow.
You need to cycle power on the monitor in order for it to come on.
Correct?

If correct, check the following:

Make sure that the monitor cable is fully seated in the video connector.
It would be worth the time to inspect both connectors for bent or damaged pins.

Check the monitor settings for any kind of power off modes.

Is the PC plugged into an outlet strip, and is the outlet strip turned off after the PC powers down?
If so, and the monitor has a "soft" power button, it would default to the "off" state.

Chas

Usually, when the monitor powers itself off the way you describe, it is an indication that the video card is sending an unsupported refresh rate signal to the monitor.

Have you tried this monitor on another system?
Or, another monitor on this system?

Since you say that this started happening after changing the hard drive. It may be wise to open the case up.

With power off, make sure that ALL plug-in cards and cable connectors are fully seated.
Remove and re-seat your RAM modules.

As a side note:
If the system speed is 166 MHz, it is either a Pentium or Pentium MMX.

The slowest PII was 233 MHz.
I don't remember for certain the slowest PIII, but I think it was in the 500 MHz range.

Chas

do you think it is work trying another video card?

If another monitor works okay on the system, then the video and internal connections are fine.

Either the motherboard is sending out a refresh rate that the monitor does not support.

Or, the monitor is set to a specific refresh rate, and will not switch to the "standard" mode that the BIOS uses at POST.

Looking at the HP MX90 manual, try this:

Restoring Factory Adjustments
To restore all parameters to the original factory
values:
1 Turn the power off.
2 While pressing the Plus (+) button, turn the
power back on.

Then see if the monitor functions at boot.

If the monitor now turns on properly, a mode was set that prevented the monitor from operating at the resolution and refresh rate used by the BIOS.

Chas

I tried resetting the monitor to the factory defaults, but it still did not power up at boot.