Windows 7: performance issues going from x86 to x64

I have an HTPC that I use for watching Netflix and hulu and photo editing. I have been using windows 7 Pro x86 for about 3 weeks flawlessly. I have done a clean install to Pro x64 and now my video quality in Netflix has become almost unwatchable. I just did internet speed test with Speedtest.net - The Global Broadband Speed Test and my average is 15Mbps. What could be the problem?

I can only say I've no problems with Netflix videos (I'm Windows 7 Ultimate x64). Install latest vidcard drivers? Need latest mobo drivers? BIOS flash?

I did the vid card, how do you find mobo and bios flash

Quality was dvd or better in pro 32, now its like boxes every time something moves

Go into Device Manager and uninstall the Display Adapter > reboot and let Windows install the default VGA drivers. Make sure you've downloaded the correct vidcard drivers and noted their location. Then Device Manager > right click Display Adapter > Update Driver software