Tried switching HD 5770 to HD 6770, fans just spin and no display

MSI 770-C45 AM3 AMD 770 ATX AMD Motherboard
OCZ ModXStream Pro 500W Modular High Performance Power Supply
XFX HD-577A-ZNFC Radeon HD 5770 (Juniper XT) 1GB 128-bit GDDR5 PCI Express 2.1 x16 - old video card
ASUS EAH6770/DI/1GD5 Radeon HD 6770 1GB 128-bit GDDR5 PCI Express 2.1 x16 - new video card

Replaced failing Radeon 5770 with Radeon 6770 and now it won't work.

Motherboard LEDs turn on, CPU and case fans turn on. Graphics card fan turns on and then keeps cycling faster-slower every five seconds or so. No signal through VGA or DVI.
The problem persists even when I put the old card back in. What could have gone wrong?

Any ideas, anyone?

Tried:

• Reseating RAM
• Resetting CMOD
• Reseating both cards
• Different cable from PSU to card
• Dusting all components thoroughly

The card's video ram was bad. Various objects in games would have a rainbow texture, screen effects like i.imgur.com/EdIOZ.jpg would show up frequently, and Video Memory Stress Test reported so many errors that they blocked out the sun.

you can't put 5770 and 6770 in crossfire because you can't switch 5770 to 6770 by installing 6770 bios to 5770, it will not work, 5770 will work only with its bios (5770 bios only).

5770 and 6770 crossfire is officially supported by AMD. Only requirement is you put the 6770 in the main slot. However by reading your post i know that is not the problem. I cant post a link or img yet but if you look at the official crossfire application chart by AMD you can see for yourself.

Make sure the card is fully seated. Next i would see if you can try the cards in another system to rule out the cards not working. If the cards work then i really dont know. Could be your motherboard took a static shock in the exchange. The working 5770 you pulled out should still work despite any GPU exchange conflicts.

Thanks for the thought, but this isn't a crossfire issue. It's a no-post issue, and a new power supply didn't help. Does anyone else perhaps have a diagnosis?