Imac G5 won't boot?

[dagogo]

Hi,
My 17" ALS Imac is not booting (tiger OS).
I will preface this by stating the hard drive has been whining and making a lot of noise for the past year or two.
Anyway, a few days ago it froze up and I had to pull the power plug. I tried to restart and got a plain gray screen and saw a question mark.
Now when I try to retsart I get a plain gray screen with the following message:

Invalid memory access at: 0SRRO: (then a long address)
WELCOME TO OPEN FIRMWARE
To continue booting type "mac-boot"
To shut down type "shut down"

After I type mac-boot the hard drive (or cd drive?) starts racing quite loudly and then it freezes up and displays a grayish screen with dozens of short, yellowish, horizontal lines and I have to pull the plug again.

I have been anticipating a hard driver failure for a while so at first assumed that was the problem, but now I see this memory error and am not so sure.

I was planning to purchase a 1 TB drive and maybe upgrade the OS at the same time . Basically I am wondering if I should go ahead and do this or run some additional diagnostics first in case it's something else? Thanks for any input.

 

[iMAVERICKam]

Do you still have the original discs, which include Apple Hardware Test?

 

[dagogo]

Yes, I should still have them somewhere...

 

[Plymouthbreezer]

Yeah, see if you can find those discs.

Memory issues apparently. Did you try pulling out the RAM?

 

[dagogo]

Ok, I'll look for them when I get home.
I suppose they have some sort of diagnostics?

I added more memory about a years ago and I still have the old 512 stick that I replaced with a GB stick. I could switch those out too.