Won't Boot Past Apple Logo, White Screen, HELP!

I replaced the logic board because at the time I wasn't sure what the problem was so I ordered both the logic and video card. Well the logic board came and the video card was on backorder so I figured I'd rule it out by swapping it. It did not make a change in the problem so I sent it back. This was done well before I knew about how to boot into diagnostics.

I still have the same problem as mentioned above and think it could be the video card, it is the only thing left.

I was reading the results from the built in 24" display. I can run the diagnostics but trying to boot from the install disk as to try to reinstall the OS I can not do, nor safemode, I get same problem as mentioned above.

Are you telling me the screen is fine in diagnostic mode? Is there any way you can hook up an external monitor? I know you think you have a hardware problem, but I've heard nothing that convinces me of that.

I tried hooking up to my 46" TV via HDMI converter from back of iMac but I had no signal out according to my TV. I wasn't sure if there was something I had to do to get the video to be external other than to just hook it up. Is there a key stroke I need to do to get it to switch to the external monitor while booting?

Normally, I can't boot into anything other than Command S and Diagnostics, everything else just gives me a white screen after the apple disappears (around 10-20 seconds). I can still hear the hard drive running in the background as it is probably continuing to boot but only have a white screen.

My thought is that the video card works ok under low res but as soon as it requires high res it just doesn't put out and I get the white screen. Does that sound logical?

I wouldn't count the TV as a reliable test unless you've done it before you started having problems. I think there's a very good chance that your problems are software related.

As a side note, I really appreciate you taking the time to help me on this one. I am so frustrated at this point. I was a PC guy since the Mid 80's, building systems on the side for friends, co-workers, and family. My brother-in-law talked me into Macs in 2006, hence my late 2006 iMac and I loved them ever since. I try to stay away from PC's as much as possible but I still work on them for people on the side for old times sakes. Anyway, I am still learning about Macs and how they work and all the ins and outs so that is why I may sound somewhat less educated with probably common Mac commands and abilities. I actually went out and bought a used Mac Mini to use in the mean time (Mid 2010) in hopes I can get my 24" one fixed up. Well at least until the end of the year when I can hopefully afford a new 27", wife willing... ha ha...