Question 2 video cards: fans spin but no signal

Jan 24, 2021
i have low profile desktop(ddr3, i3 540, 4gb ram.) after a thunderstorm and quick brownout this midday, my video card(gt635(1gb, 64bit, dd3) was fried. i reseated it, no signal. i managed to get a signal once but the card turned off and the signal was lost as the pc continued to boot. now, no signal again. i used a backup gpu(gt8300(256mb, 64bit, ddr2) until i found and received the suppose to be replacement, an amd radeon 7000(same specs as the gt635.) the seller did not have a pc to test it, it was sold for a low price, and despite whatever i do(clean contact, reseat, thermal paste) it won't show a signal like the gt635. i've told the seller that its defective. despite tips, we could not make it work so we agreed that it was defective and and i've already been refunded.

everything seems ok with my rig apart from the video card issue. it makes me think if my pc now is not able to use ddr3 video cards or has a similar weird problem. it doesn't seem to the video card slot since my gt8300 is working ok. the 635 and 7000 exhibit the same problem: the fans spin but there's no signal; could the power supply now be inadequate for those cards but adequate for the ddr2 gt8300?
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