Hi,
Are there any beeps when you boot up i.e. POST test results.
When you boot up your machine the Power On Self Test tests various parts of the PC including the PCI bus, Video etc.
Normally if the MB doesn't communicate with the Video card (because its faulty or the bus is faulty) the POST test will beep. This is because the vga bios has not been actioned.
See for info on POST tests
Have you tried allowing the PC to boot up all the way, and, if you have a sound card in a PCI slot, do you get any sound when windows starts. If you do then maybe the PCI bus is OK.
Does your motherboard have an onboard VGA controller ?. This would have to be disabled if you are using an add on VGA card. This is done through the BIOS, CMOS settings. Only problem is you can not see the screen. If it does you would need to connect the monitor to the onboard VGA, diasble it in the BIOS and then connect it to the add on VGA card.
Before investing in a new motherboard, and as a last ditch effort, I would switch of the power, remove the CMOS battery (possibly even short out the battery terminals). Replace the battery and restart. This should set everything to factory default. Who knows maybe you're CMOS settings got screwed up.
Any Help, Yes/No let me know
Regards
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Is not a fool a wise man in his own eyes - Proverbs