|The term CARD is frequently mis-used.|
A video adapter is a CARD ONLY if it is a video chipset on a physical board (PCB) in a mboard slot that can be removed. Onboard video or a USB or firewire connected video adapter IS NOT A CARD !
"gigabyte hd 5770 graphics card"
ATI Radeon™ HD 5770 System Requirements
- 450 Watt or greater power supply with one 75W 6-pin PCI Express® power connectors recommended (600 Watt and two 6-pin connectors for ATI CrossFireX™ technology in dual mode)
ATI CrossFireX™ technology in dual mode = e.g. two video cards in mboard PCI-E X16 slots with a single video chipset on each, or one card in a mboard PCI-E X16 slot with 2 of the same video chipset - a X2 card.
"I have a 550w PSU ..."
Your power supply has more than enough capacity for one HD5770 video chipset on one card, but you MUST connect a 6 pin PCI-E wiring connector from the power supply to the socket for that on the HD5770 card.
Or, if the socket on the card is 8 pin, you can connect either
- a 6 pin PCI-E wiring connector
or - 6 + 2 pin PCI-E wiring connectors - the two pin one is beside the 6 pin one in the same bundle of wires
- or an 8 pin PCI-E wiring connector.
If your power supply is older and does not have any of those connectors on it's wiring, you can buy an inexpensive 6 pin PCI-E connector to two (male) molex connectors wiring adapter, and connect it to two spare larger (female) molex connectors you normally plug into drives.
You can probably buy that locally at a place that has lots of computer parts.
If you didn't connect that, you will get no video from the card, and a continuous beep, or a long beep, or a pattern of beeps, depending on the mboard's bios version, that indicate(s) a video problem.
Always unplug the computer or otherwise switch off the AC power to the computer when you are going to be fiddling with plugging in or unplugging any wiring connections or components inside the case.
"gigabyte ga-h55-ud3h motherboard"
Your mboard supports Hybrid Crossfire video.
When a mboard supports the Hybrid video feature (Hybrid Crossfire - ATI video both onboard and on the card in a slot - or Hybrid SLI - NVidia video both onboard and on the card in a slot - the mboard's main chipset that supports the Hybrid video feature usually supports one or the other, but there is at least one main chipset that supports both), the onboard video on the mboard is NOT necessarily automatically disabled when you install a graphics card in the PCI-E X16 slot, like it is with mboards that do NOT have the Hybrid video capability.
Hybrid Crossfire = when you install certain specific ATI video chipset cards in the PCI-E slot , BOTH the onboard video and the video on the card will work at the same time by default - the onboard video still shares some of the ram installed in the mboard - the card in the slot uses it's own ram on the card itself.
You can alter that situation by changing settings in the bios Setup (see below).
- if you install an ATI video chipset card in the PCI-E slot that has a video chipset that is NOT supported by the Hybrid Crossfire feature.....
(or, probably, if you install ANY NVidia video chipset card in the PCI-E x16 slot on a mboard that has Hybrid Crossfire support but NOT Hybrid SLI support....)
- you may get NO VIDEO from the card in the PCI-E slot by default.
In that case, the onboard video is still enabled by the bios. If you connect your monitor to the onboard video port, you will find that you still have onboard video. (Plug in or unplug the monitor ONLY when the computer is not running.)
If you DO have that situation, (or if you do have video from the card but you want to disable the onboard video).....
Go into the bios Setup and change the setting for Primary Video or Initialize Video first or similar to PCI-E or similar, Save bios settings, then the card in the PCI-E slot will produce video, the onboard video will be disabled, and the ram installed in the mboard will no longer be shared with the onboard video.
I had to do the latter with an Asus mboard that supports Hybrid Crossfire when I installed a HD-AIW video card in the PCI-E X16 slot - it's ATI video chipset is not supported by the Hybrid feature - I got no video from the card in the slot and no mboard beeps by default.