Q: i want to connect imac g5 mac 10.4.11 to plasma tv via hdmi, pls help me do it

I don't believe G5 iMacs supported HDMI. But which model G5 do you have?

You should be able to restore or access the computer whilst booted from the OS X
Install - Restore system DVD, and once you are past the setup so you can view

the menu bar structure of the Installer options, you can choose to change Admin

Password. That would be the easiest and probably the best way to restore access.

A few links to web site articles on this topic point to the basic & some to more advanced

things one can do, to restore or change the admin password. Some of these also say

how to access user accounts who are less than Admin.

The system install disc is your proof of software license, and key to restoring. The same

disc set is greatly helpful in troubleshooting, repairing, replacement of hard disk drive, etc.

For Snow Leopard and earlier with installer DVD

     Mac OS X 10.6: If you forget your administrator password

     OS X- Changing or resetting an account password (Snow Leopard and earlier).

For Snow Leopard and earlier without installer DVD

    How to reset your Mac OS X password without an installer disc | MacYourself

    Reset OS X Password Without an OS X CD — Tech News and Analysis

    How To Create A New Administrator Account - Hack Mac

{Above covers some that I had bookmarked, & others; this list compiled by user Kappy.}

A site such as Everymac.com can provide you some hardware information of the computer model

you have; then you could look into display adapters or a different display for use with that iMac.

If your supplied info on iMac G5 1.8GHz (limited though it is) should be correct so far, you may find

Everymac in search result page: https://duckduckgo.com/?q=everymac+iMac+G5+1.8GHz+&t=ffsb

Also, for your own information beyond what 'About this Mac' can tell you, from Apple menu bar,

(and the System Profiler, access from there, via 'More Info' button) you may also use the serial

number of the computer and use an online lookup to see more info about the specific computer

you have; do not post the serial number in a discussion thread, though. An example site, follows:

• Mac Serial Number Info - Lookup your Apple Serial Number (helps to identify hardware configuration)

https://www.powerbookmedic.com/identify-mac-serial.php

The plasma TV would need to connect via some other non-HDMI adapter; does it have other ports?

There is a fair chance the idea may need revision, and perhaps different unit found for 2nd display.

In any event...

Good luck & happy computing!

The G5 can't support HDMI. Even if you get get a DVID dual link to hdmi convertor cable and it will not work. http://www.amazon.com/Gefen-HDMI-Cable-Male-Male-CAB-DVI2HDMI-06MM/dp/B0002CZHN6 . 

You would have to buy a apple mini vga to DVID converter cable even if it put out digital signal and I can see no sigh that Apple made such a cable.

Some older Plasma TVs might have SVGA connectors on them, but the output on the iMac G5 may max out at either 1024 x 768 or 1280 x 1080 depending on which model it is.  You won't get widescreen resolutions out of it.    To find the external resolution, http://www.everymac.com has that information listed.

Yes, analog options only.