I have the eVGA GeForce 5700 LE but mine has 256MB of memory on it. But also have a P4 2.6Ghz processor, 120GB Ultra DMA hard drive, 1.5GB RAM, the 78.01 driver and Direct X 9.c
I have no problems running Nightlife on my computer with that card, the problem might not be your video card.
Have you checked your game options to see if anything is turned off that wasn't before or if any settings are on low that shouldn't be?
Sometimes a graphical problem like that can be caused by the driver. Generally, if your driver is working the way it's supposed to with your programs, there's not usually a need for you to update the driver unless the new driver is specifically fixing an issue with your card model (and older card models aren't always compatible with newer drivers). I would say try rolling the driver back to the driver you had before, but since you've changed your system I don't know if that will work. If the driver information gets stored on the hard drive, then it might work, but I dont know if that's how all that works. I'm not a computer wizard, just an apprentice heh but I dont see how any harm could be done by trying since if it doesn't work you can simply re-update the driver.
Try following Bangelnuts' suggestion and see if you can rule out it being a processor issue. If that doesn't fix it and it's not your game options I would suggest that you try checking your RAM (try going to
www.memtest.org and install their RAM tester) to make sure none of it got damaged when your motherboard got fried. And regardless of it working properly or not I would highly suggest increasing your RAM if you can afford it (you can find some good deals on the internet), I know the minimum requirement to run NL is 256MB RAM but that's probably only enough to run it at its lowest settings (I'm not inclined to find out...); you have 512MB but still this is a very graphic intensive game which usually translates to being memory intensive as well, I have 1.5GB RAM and 256MB video card memory and there are settings in my game that are turned off or set at medium settings whereas prior to NL everything was turned on and set to max settings.