Screen Freezes and Becomes Pixelated/Fuzzy. Video Card Problem?

Recently, my screen will just freeze and become covered with lines/boxes to the point where you can't tell whats on the screen. This usually happens within minutes of booting up. However, sometimes, everything will work fine for maybe half an hour and then it will happen. I know for sure it is not a problem with the monitor.

I assume this is most likely a video card issue, but I didn't want to buy a new one before confirming. I attached a picture of what the screen looks like after it freezes.

The card I wanted to buy to replace the old one is EVGA GeForce GTX 650.I would also like to confirm that this card will be compatible with my current setup. From my understanding, the current PSU and motherboard will accept it, but I don't know if anything else can affect this.

Thanks in advance.

Computer Details:

Windows Vista Ultimate 64-bit
4GB DDR2 - Corsair XMS2
Intel Core 2 Duo E7400 Processor BX80571E7400 - 2.80GHz, 3MB Cache, 1066MHz FSB, Wolfdale-3M, Dual-Core, Retail, Socket 775
Intel DP43TF Motherboard - Intel P43, Socket 775, ATX, Audio, PCI Express, Gigabit LAN, USB 2.0, Serial ATA
BFG GeForce 9800 GT Video Card - 512MB GDDR3, PCI Express 2.0, (2) Dual Link DVI, HDTV, VGA Support
Ultra LS500 Lifetime Series 500W Power Supply - ATX, SATA-Ready, PCI-Express

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