iMac 24 2.33 issues- REALLY wierd

OK, here is the largest and strangest set of issues you have ever heard of. Nothing compares, and I dare you to fix it!

I got my hands on an iMac 2.33 (white), however it was just the back, stand and logic board- It had a sticker that read, "turns on, chines, no boot"

SO, I browsed for someone with the rest of it to see what the issue was, and to see if I could fix it. I assumed it was a bad HDD...

I got a 24 2.16 iMac, and I took it home and took all the parts out. Turns out that the iMac would phisically freeze upon attempting to boot and the graphics card had problems. The CPU was working fine.

SO, I took out the graphics card and swaped in the other card. now it turns on, chimes, goes to the grey screen with logo, boots fine with no lagging in the wheel, but then freezes on the grey screen- like the one just before the blue, which goes to the desktop.

STRANGEST YET, when I took a look at the light, it would go off at the boot as normal, then after being stuck at the grey screen for no more than a minute it would turn on and stay on, no flashing.

I have tried the other logic board from the other copmputer (which was suspected to be iffy) and it does the same.

I'm also not computer illiterate, so here's what I have done-

Booted normally

Booted safe mode, safe issue as above

Booted verbose mode, nothing wrong, no errors and it continues to the grey screen

Tried my back up of the 10.6 disk which is on a USB drive, freezes on the spinning wheel- maybe USB is an issue but I do not have any actual disks or a DL DVD

Swaped RAM but that would cause a loud beep if it was an issue.

Here's the catch, and I'm not sure if its the issue- the internal drive was originally from another computer, an iMac 20 core duo. Could it be some driver issues? Its a 750GB drive but size shouldn't matter...?

Please let me know what you think about this cluster of issues. In the meantime I will try to eliminate some of the variables.