ATI Radeon HD 4800 is compatible with your motherboard but there could be problem with power supply because those graphic cards are requesting stronger PSU.
Here in this link you can read PSU requirements for HD 4800 series of Graphic cards:
no video driver present since a reformat and can't seem to download, motherboard is a k8m400 for an...
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no video driver present since a reformat and can't seem to download, motherboard is a k8m400 for an acer desktop