dharma's AGP slot bad - maybe

Dharma refused to boot a few months back, beeping a lack of display. Tried PCI card, still no go. So snuck in an old ISA VGA card to make it boot. Only 16 colours, but boots. Today tried other AGP cards - Matrox Marvel G400, G200 - no go. Tried the PCI card, still no go. Then tried the PCI card in a different PCI slot + ISA card, booted, saw that the PCI card was listed in device manager. Then tried with PCI alone, booted OK, recognised the Sis 6215 card and loaded the correct driver. So, restored the system to using the PCI Sis card. Maybe the AGP slot has gone bad?