Need help choosing new graphics card

I've been having many problems with my computer running at all. I started replacing components. First was the mobo and processor. I installed an Asrock 4CoreDual-SATA2 because of it having an AGP slot for my ATI All-in-Wonder 8500 I wanted to keep using. The original processor was an AMD 2700+. I was not impressed with this processor from the beginning so I installed an Intel Core 2 Duo E6550. After reloading Windows XP from scratch, my PC ran for a few weeks. Now sometimes it will boot up and sometimes it won't. It will even freeze while in Bios. My next step now is to replace graphics card. The reason for this is, once the computer is on for a couple minutes, the screen gets too blurry to read. The cooling fan on the card is also bad. The problem I am having is choosing a graphics card. This Mobo has a PCI-E 4x slot along with the AGP. All the cards I am finding for PCI-E are either PCI-E 2.0, PCI-E 16x, or PCI-E 1x. What can I use in my slot? I don't do gaming, but the main purpose of the computer when I bought it was for video editing and transfer from video tapes to DVD. It has not been good at it since new. It was bought when the AMD 2800+ had just came out so it wasn't using outdated components. Any suggestions for graphics cards or my other dilemmas would be greatly appreciated!