Imac (2008) not booting. No Startup tone.

[Alphaeus47]

When the on button is pressed The fans start, but the screen doesn't even turn on. The Optical Drive still takes in Disks.

No sound other than the fans, CD Drive (and possibly the HDD - hard to tell)

It's running 10.5.8
3.06GHz
4GB DDR2 @ ~800MHz
nVidia GeForce 8800GS
500GB HDD

Tried:
Turning off and on (hey… it works sometimes.)
Resetting PRAM, Pretty much impossible as I don't get the first startup tone (also using wireless keyboard, doubt that'd work until it's started booting.)
Inserting Snow Leopard Disk…

Without any picture, sound, or input i can't think of a whole lot else i can do.

Only recent change to hardware or software was attempting to use a wireless Microsoft mouse… Which didn't work, so I swapped it back.

Any suggestions?

 

[Hellhammer]

http://guides.macrumors.com/Mac_doesn't_boot

 

[Alphaeus47]

Well it's blackscreening… it seems like a logic board thing. But its still powering USB devices, and it's still regulating fan speeds. That's the confusing part…
Thoughts?

Edit: Oh, and the hard drive is turning on… it's just that nothing is happening.

 

[Hellhammer]

Well it's blackscreening… it seems like a logic board thing. But its still powering USB devices, and it's still regulating fan speeds. That's the confusing part…
Thoughts?

Edit: Oh, and the hard drive is turning on… it's just that nothing is happening.

Could be display, GPU or the logic board. Your only option is to let Apple have a look at it

 

[Sun Baked]

Did the cat walk across the keyboard and turn off the sound along with dimming the screen.

When the machine don't bong, plugging in the wired keyboard and trying a PRAM reset is about the only thing you can do.

If the sound is off and the logic board is working, it'll bong when the PRAM resets and it goes through a restart.

---

The BONG is part of the power on self test.

All we can do after that is reset the SMC, and check the RAM ... otherwise checking the diagnostic LEDs is in order if the machine has em.