Go to Device Manager and see if you have any conflicts.
Sorry, it's hard to resist those sometimes. Here's a couple shots in the shadows. Try to think of what you did recently. Any new hardware or drivers? Disable onboard peripherals, if equipped, one by one, with reboots between to check on it. If it still doesn't come up, take out all PCI cards but the NIC or modem, and try again.
I have been known to make mistakes...from time to time. I could be totally off.