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#11
How do you mean low voltage. Oh as stated by polarbear: With a more balanced power PSU. If the card is demanding more power than the rail on the PSU can carry it will fail or show signs. It's an educated guess as to the PSU being an issue. It would be great if you can get your hands on a known working unit large enough to handle you system and test it. Use this link as a minimum guide.
eXtreme Power Supply Calculator
Wish you were close by as I have a working 600w we could try !