ビデオカードの交換とケース内部の清掃が終了. 以下のようなxorg.confで正常に動作している…

Section "ServerLayout"
	Identifier     "X.org Configured"
	Screen      0  "Screen0" 0 0
	InputDevice    "Mouse0" "CorePointer"
	InputDevice    "Keyboard0" "CoreKeyboard"
EndSection

Section "Files"
	RgbPath      "/usr/local/lib/X11/rgb"
	ModulePath   "/usr/local/lib/xorg/modules"
	FontPath     "/usr/local/lib/X11/fonts/URW/"
	FontPath     "/usr/local/lib/X11/fonts/Type1/"
	FontPath     "/usr/local/lib/X11/fonts/TrueType/"
	FontPath     "/usr/local/lib/X11/fonts/TTF/"
	FontPath     "/usr/local/lib/X11/fonts/OTF/"
	FontPath     "/usr/local/lib/X11/fonts/terminus-font/"
	FontPath     "/usr/local/lib/X11/fonts/bitstream-vera/"
	FontPath     "/usr/local/lib/X11/fonts/local/"
	FontPath     "/usr/local/lib/X11/fonts/misc/"
	FontPath     "/usr/local/lib/X11/fonts/75dpi/"
	FontPath     "/usr/local/lib/X11/fonts/100dpi/"
	FontPath     "/usr/local/lib/X11/fonts/cyrillic/"
EndSection

Section "Module"
	Load  "extmod"
	Load  "record"
	Load  "dbe"
	Load  "glx"
	Load  "xtrap"
	Load  "GLcore"
	Load  "dri"
	Load  "freetype"
	Load  "type1"
EndSection

Section "InputDevice"
	Identifier  "Keyboard0"
	Driver      "keyboard"
	Option      "XkbModel" "pc101"
	Option      "XkbLayout" "us"
EndSection

Section "InputDevice"
	Identifier  "Mouse0"
	Driver      "mouse"
	Option      "Protocol" "auto"
	Option      "Device" "/dev/sysmouse"
EndSection

Section "Monitor"
	Identifier   "Monitor0"
	VendorName   "MEL"
	ModelName    "RDT176S"
	HorizSync    31.5 - 69.0
	VertRefresh  56.0 - 75.0
	Option       "DPMS"
EndSection

Section "Device"
	Identifier  "Card0"
	Driver      "ati"
	VendorName  "ATI Technologies Inc"
	BoardName   "RV350 AS [Radeon 9550]"
	BusID       "PCI:1:0:0"
EndSection

Section "Screen"
	Identifier "Screen0"
	Device     "Card0"
	Monitor    "Monitor0"
	DefaultDepth 24
	SubSectionSub "Display"
		Depth     24
		Modes     "1280x1024"
	EndSubSection
EndSection

Section "DRI"
	Mode 666
EndSection