If this occurs with both Windows and Linux, it's most likely a hardware problem (something about the boot process is causing the monitor to lose signal). Check your cables, make sure the videocard is firmly seated in the slot, and make sure that your BIOS is set to look for the correct card first (if your motherboard is capable of choosing between AGP and PCI slots for video input, and one of your two cards is in fact an AGP card).
What I suspect is that your S3 SuperSavageDDR is being chosen as your main video input, which I would imagine is not appropriate (does that card even do 2D?). What you want is for both OSes to recognize your ProSavageDDR as the main card, and the SuperSavage as a supplemental card.
To be honest, I'd just remove the SuperSavage temporarily, install my OSes and get them working, then re-insert the SuperSavage and figure it out from there. But I'm a lazy bum
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