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?