Windows 7 Limited Connectivity Wifi Problem

My desktop computer is running Windows 7 Ultimate. When I first installed windows I could connect and stay connected to the local public wifi connection that my town provides for residence to use free of charge. I installed a bunch of windows updates (maybe a coincidence) and now when I connect to the internet it works fine until i try to watch videos ie youtube or try to download a file..as soon as i attempt any one of those my connection shows limited connectivity. the signal strength is still excellent and it happens even when I swap out usb wifi adapters. I have two usb wifi adapters and they both work fine other pc's with windows xp and have been used on other windows 7 pc's with no problems. I've tried everything i can think of and have searched google for a solution but have yet to find one.

Any help would be great..Thanks