This is a list of compatible graphics cards used on various models historically.
GT660 > GT960 > GT1060
GT9800 > GT450 > GT460 > GT550Ti > GT650 > GT750 > GT1060
2RU units + TC40
GT440 > GT640 > GT740
Mini + TalkShow
GT7300 > GT9400 > GT220 > GT430 > GT550
Please download and install older Nvidia drivers, preferably dated from when unit was sold. Below are known tested versions.
GT 740 = version 340.52
GT 650 = version 306.97