I recently ran into some computer troubles and had to replace some parts. My replacement motherboard
(SUPERMICRO MBD-C2SBA+-O LGA 775 Intel G33 ATX Intel Motherboard) seems to be working fine; with integrated video everything boots up and runs well. I also needed to replace my graphics card (Sapphire Radeon HD 5770 1GB PCIe DDR5 DVI / HDMI), when its installed my monitor receives no input and strangely accessories connected to the motherboard recieve no power (usb keyboard and mouse). Everything connected directly to the power supply still runs (cd & hard drive, graphics card, case fans, the motherboard itself seems to).
No beep code, just no signal. When my old (fried) gfx card is put in a beep code exists. After disabling integrated vid through BIOS and having no gfx card in it gives a beep code when starting. So clearly it is recognizing the card otherwise it would give a beep code as well.
I tested the new graphics card in another computer to confirm that it does work.
The most puzzling thing to me is the fact that the USB accessories don't recieve power.