OS X 10.4 won't reinstall on iMac g5

I have the last imac G5 built, and its been running fine for a few years, but I noticed that its been running slower than when I got it. I am trying to re-install tiger from a retail disk, and from a burnt disk and none of them work. When I restart and hold down the c button, this is what I get,



The retail disk version is 10.4

do you have a g5 retail disk? most of the available ones are intel. it should say on the side of the box.

What retail disk? The DVD that came with the iMac? A Full Retail TIGER 10.4 DVD?

Yes its a full retail disk, I even wiped the hard drive from another mac, an Intel . And installed the beta version of leopard from the intel mac (Because the retail disk won't work on the intel mac). Leopard runs on the Imac G5 ok, but I try to put back on Tiger from the reatil disk again and the same thing happens.

It sounds like the DVD drive in the iMac is having issues reading the 10.4 Tiger DVD. Look at the surface of the DVD. Is it scratched? Dirty? If so CAREFULLY clean it. Otherwise there is no reason I can think of why it will not read the DVD unless the DVD drive is messed up or the DVD itself is dirty. Do you have any sort of Firewire DVD drive?

I would be careful discussing Leopard here on the forums unless you are a developer as it's not legal to have a copy otherwise and against forum rules.

The only time I've seen that screen before is when my college tutor mixed up the discs from a G5 iMac with a G4 eMac and the hardware check failed.