I recently added an Ethernet card to my PC at home.* Now whenever my computer hibernates, it doesn't wake up properly.** If I take out the Ethernet card, the power management starts working again. On the other hand, the computer has no reason to exist. Oh, the irony.
The card doesn't appear to have any jumpers on it. My next guess is, buy another Ethernet card (they're cheap) and see if it fixes it. Any other suggestions? Ask your friends. :)
* Long story—Yes, it came with an Ethernet port, but stopped working at some point, and as it's an on-board Ethernet port, I figured there was no hope of fixing it without obliterating my computer. Besides, I don't have a multimeter anymore. Anyway, since then I've been using my USB port instead, but my new router will have none of that nonsense. And honestly, who can blame it.
** I hit a key, and I know it knows it's supposed to wake up, because the fan turns on; but it never gets to the point of actually displaying anything on the screen.
P.S. The computer is an HP Pavilion, if anyone wants to avoid buying one at all costs.