these are what i can think of
Its usually rare that something changes in the power management settings of your computer, but maybe check and switch some options and see if it restores the correct function of the wireless.
above is the default lan adapter setting. i think the wireless adpaters would have additional values for power output and channel.
you normally dont have to bother with the default settings, but maybe for your problem, try unchecking all three options (you wont need them anyway). you can always revert back to the default settings later.
just a thought, set the power output to maximum, and the channel setting to G only. also, set your wireless router to "G" only type of wireless broadcast.
you might have already checked on this, but make sure the FN + Fx key on your laptop keyboard works fine.
uninstall, reboot, and install latest wireless lan adapter drivers?
if your wireless adapter has a wifi management program, maybe try using it instead of windows.
as for the persistent problem with even the USB wifi, i would suggest checking it too with the power mangement settings.
while its not common to see virus/worms that might have direct effect on your network connection, do a virus scan too in safe mode.
good luck on this, feel free to let us know if you have updates