I would add more RAM if possible just to cover 64-bit capability. Plus, check cooling is well maintained. If no error pop-up, then the system is basically trying to keep up. The reason I mention more RAM is it becomes a buffer in order to handle the stream. While, I think your video card is capable, if its not well cooled, it will start to falter. Freezing PCs are hard to fix as no real clue is present. I would at least allow it to remain in freeze state and see if it recovers giving at least 10-15min. more before rebooting. You can check your error/event log and review it.
http://www.windows7update.com/Windows7-Event-Viewer.html
Further, the AMD cpu maybe at fault. Check online and see if yours has any history or patches that may cover the issue. Also, heat is very critical for AMD cpus and chipsets, so its a possibility as an issue. Also, is this direct or wi-fi connection? Why, because wi-fi connection can vary for whatever reason and could be hitting a sore point.
tada -----Willy 
First off, my hardware:
AMD Phenom XII 955 no overclock
Asus M4A79T Deluxe Mobo
Corsair CMPSU-650 650w PSU
VisionTek Radeon HD4870 512MB
LG WH08LS20K 8x BluRay burner
WD Caviar Black WD7501AALS 750GB 7200RPM HD
Mushkin Blackline 4GB (2x2GB) DDR3 1600 SDRAM
Encore ENLWI-N PCI 2.3 Wireless Adapter
Monitor Vizio VX32L
Windows 7 64-bit
Norton AV
My computer will freeze and become totally unresponsive, mainly when watching HD video on youtube, downloading torrent files via uTorrent, or if my background is set to a photo album and rotating pictures. Those are the 3 most common ways it will freeze right now, though it happens very occasionally other times. No error messages, the screen just freezes and I get static coming through my speakers. All of my drivers are updated, and in the past I have reformatted my HD for a fresh install, but still getting stuck. I can watch full 1080P video no problem in Media Player classic and Windows Media player, but when I try to stream anything in HD, I have problems. No issues watching youtube at 480p or lower, but if I dare click for 720P it will play for a little bit, maybe even make it through a whole video, but the inevitable always happens. I have tested the memory with Memtest86+, no issues there. I have also ran the trial version of PCMark Vantage and got a score of 7599. Nothing looks fishy from that, except it says my graphics memory is 1MB. If needed I can try to provide a link to the online results from that test. I am about to run 3D Mark Vantage also(trial version) but have a hard time believing it may be my video card, since I have no issue watching HD Video any other time other than in a browser and have no issue running the Unreal Editor Kit. I currently am running IE8, but have had the same issues with Firefox, actually seemed to have more issues with Firefox which is why I went back to rocking IE8. I also thought the problem somehow might be the wireless adapter couldn't handle the bandwith of HD video, so I plugged the computer directly into the router, and still had issues. I have also run CC Cleaner to fix any registry errors. I have to restart the system to be able to use it again. Anyone have any ideas? Any other tests I can run to find the problem? If more info is needed, I will post it right away. I would greatly appreciate any help. Thanks for your time.
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