Every computer is different. It could be F2, F8, F10, F12 and more.
There are a million things you can do
You can go to you device manager and is there a yellow ? next to it?
You can try going through your controll panel. Add new hardware, and hard wire it if you can
Are you wireless on your desktop?
You can use the system restore as you may have run into a conflict. Start>All Programs>System Tools>System Restore
The bottom is what I'd do first personally. Just go back a couple days