iMac Stuck at Boot Logo w/ White Bar through Logo URGENT!!!

Hello, I have an iMac Model: A1225. At first, my problem was that on start-up, the iMac would not get past the boot/logo screen, and then all of a sudden it would go to a gray screen with three thick, white, jagged bars running through the screen. I tried to boot from a recovery USB and DVD, but it was no luck. It would not boot from anything. I ran a disk check on the hard drive from single-user mode, and it said that the hard-drive was okay, but I decided to change the hard drive and the memory anyway. I put a brand-new, fully-funtional, formatted hard drive with Snow Leopard that booted fine on another computer and brand-new memory. Now, when the computer gets to the boot/logo screen it gets stuck here with a thinck wite bar running through the apple logo. Please Help! I will also post a picture. Thanks Guys!