Wont boot on its own, wont boot with install disc,

Did you read the Apple support page on this problem? they are really good in helping: Troubleshooting My computer won turn on

Sounds like the monitor screen is shot! That's not good with that all in one computer! If it were a laptop changing the screen is easy! I hope you get it to work! I am searching for info for you! Hang tight!

boot to osx install boot disk or boot usb. on the top bar in utilities chose reset password and reboot afterward

This is the closest thing I found

http://www.ifixit.com/Guide/Repair/Installing-iMac-Intel-20-Inch-EMC-2133-and-2210-Hard-Drive-Replacement/1008/1

Checking the power supply isn't the easiest thing to do, it involves pulling apart the entire machine.
You can try resetting the SMC, unplugging all power, hold the power button for 5 seconds, replace power, then attempt to turn on.
if it still won't turn on, and assuming you didn't get AppleCare or it is expired (past 3 years) it might be worth taking in to an Authorized Apple Repair Facility and see if they will check it out for free. If it is under warranty, most definitely take it in or call 1-800-APL-CARE
If neither of those are an option, Power Supply http://www.ifixit.com/Apple-Parts/iMac-Intel-24-Inch-2-4-2-8-GHz-or-3-06-EMC-No-2211-GHz-Power-Supply/IF169-002
a tear down from iFixit for the 20" model, it is most likely very similar for your model as well http://www.ifixit.com/Guide/Repair/Installing-iMac-Intel-20-Inch-EMC-2133-and-2210-Power-Supply/1006/1
Hopefully that helps. Good Luck

This is the closest guide I can find to help you.....

http://www.ifixit.com/Guide/Repair/Installing-iMac-Intel-20-Inch-EMC-2133-and-2210-Hard-Drive-Replacement/1008/1

If it only boots to a blue screen, try booting up in Safe Boot mode:

http://support.apple.com/kb/ht1455

If this does not work, boot from your install DVD and use Disk Utility to repair the disk:

http://support.apple.com/kb/ht2956

If this does not resolve the issue you may need to use your isntall disc to perform an Archive and Install:

http://support.apple.com/kb/ht1710

To eject an optical disc at startup, hold down the mouse key on a wired mouse immediately after turning the iMac on with the power button. Keep it held down until the disc ejects, which should occur within two minutes. If you hear the disc trying to eject but failing, it is physically jammed in the drive and will have to be removed by a professional technician.

It could be a hard drive problem or it could just be a software issue. Given the model, it could be running System 9 or X or both. If it is 9 it just may need to be blessed. The disc you are trying to load sounds model specific as opposed to Apple's retail discs which will load on any of their models capable of running that particular operating system. Whether it is worth fixing is really a judgement call, if you have use of a 2nd machine a hard drive / install disc can be had for cheap enough, as far as resell value, I would say no. Due to the limited information you have on the history of the machine I would suggest following these links to try and determine if it is indeed hardware or software:
Mac OS 7.x - 9.x: Troubleshooting Startup Issues

Your Mac won't start up in Mac OS X (Mac OS X 10.3.9 or earlier)