Can't boot from disk, Darwin won't take login

I have a older iMac G5 running 10.4.11..when I connected my ipad1 to iMac is when this all started...it won't go past start up, so after going to apple.com support I came here because I have tried different things to get it back up but it seems it won't do anything.
I have used the disk to try and start from but it goes to Darwin and it won't let me log in..says log in failed
I bought this iMac used and have NEVER had to use that persons admin log in, but I even tried that and I cant get past the Darwin log in failed. I don't know what to do I'm so frustrated...any help is appreciated !

The system is hosed. You will need to boot from the original DVDs, wipe the HD, reinstall the system. You should have done this IMMEDIATELY after buying the machine -- if you're not the admin then that's not really been your computer.

chas_m said:

The system is hosed. You will need to boot from the original DVDs, wipe the HD, reinstall the system. You should have done this IMMEDIATELY after buying the machine -- if you're not the admin then that's not really been your computer.

Click to expand...

That was done yrs age after I received the computer and has never been a issue...I have tried using each name & password the comp has ever had and it won't take any of them.
It does say HER name as the comp owner & I used the admin password for her and also mine. It won't take anything, keeps saying login failed

Also it won't boot from the disk, it goes to Darwin..I held down the C key to try that and Darwin again

chas_m said:

The system is hosed. You will need to boot from the original DVDs, wipe the HD, reinstall the system. You should have done this IMMEDIATELY after buying the machine -- if you're not the admin then that's not really been your computer.

Click to expand...

Hosed ?? What's that ?