Normally, with a post such as this, my first recommendation would be to insure that your wireless adapter drivers are as current and up to date as possible. Additionally, likewise with the firmware on the router. Standard, boiler plate, first things to look at and confirm that they are the most recent.
But; since your post starts with the dreaded four words "All of a sudden", I would actually first recommend a system restore, to a restore point, prior to "all of a sudden" (actual time and or date the problem first appeared.) If that doesn't help, then you might want to try forceably rolling back the driver for the wireless card in device manager.
If still no joy, then just to confirm the excellent trouble shooting you've done to this...