Hi FanacooL,

1. I wouldn't disable the onboard Video AND remove the driver. I would leave the driver there and just disable the onboard video. I suspect that might be your problem, as the BIOS cannot activate the onboard video without a driver.

2. The frame buffer is the amount of memory that the video can use to build images before displaying them. As the memory is now on your video card, I would try 64Mb, but I don't know your MoBo or BIOS. If you are still "sharing memory" all that will do is slow your computer as the system will have less RAM to play with. It should not give you the display problems that you are describing.
I believe that you are confusing this with the IGD which is tha memory address space that the onboard chipset can use.

3. That board has some quite advanced onboard graphics, so adding a lower to middle end video card may not improve things and may indeed make them worse.

4. The Intel 915 Chipset is intended to support PCI-E, (Express) so have you got the right video card. What is the exact model of your MoBo and your Video Card ?

My approach would be :

1. Remove video card
2. Reinstate onboard video and get it working
3. Install video card
4. Select the videocard in the BIOS
5. Set frame buffer to 64
6. Test it all works properly
7. Install audio card

I would also try that video card in another machine, if the above does not work............there is still the possibility that it was defective when you bought it. Unfortunately with the fall in price of components the testing standards have also fallen so more defective items reach the consumer

Good Luck