I'm not certain, but I think it might be that your new video card is overheating. Does it have a fan or a heatsink? If there are other devices in your PCI ports you could maybe rearrange them so there is more clearance for the video card. Also, install the latest driver for the video card if you haven't already done so. You should also try reseating your video card, blowing out the PCI-E slot with a can of compressed air (DON'T use a vaccum cleaner) and wiping the contacts on the video card with alcohol and a Qtip.