iMac G5 won't boot

[Cams]

I have an iMac G5 (the one with the iSight). When I switch it on, the white power light on the bezel comes on but that's it. Is there any way of running a diagnostics check on it?

The hard drive was recently replaced and I'm wondering this: what would the symptoms be of a failed HDD? On Windows I know it will say something like Invalid System Disk or No Disk Found. What would the iMac do? Would the LCD still power up even if the drive was faulty?

 

[flopticalcube]

You would still get a powered up LCD and a picture of a folder with a question mark on it. Try resetting your PRAM and PMU (remove the plug and press the power button for 10 sec). Could be a loose connection inside made when the HD was installed.

 

[Cams]

Unbelievable -- it worked! Thanks so much. Can you explain a little what parameter ram and PMU are, or provide a link to such info? It would be useful to know what i just did.

 

[flopticalcube]

Sure. PRAM is in my sig and resetting G5 SMU/PMU is here.

Parameter RAM is just a little permanent RAM that stores various configuration data. SMU/PMU is a small controller that controls various power aspects of the Mac.