Ethernet not working after power outage

A few weeks ago, I was using my computer when the power suddenly went out. When the grid came back online, I found that my computer could no longer connect to the internet (or local machines, despite Windows saying my access was "Local only".) Further investigation with Wireshark revealed that, although my computer was able to see every packet on the network, no other machines were able to see the packets it was sending.

I have a Gigabyte GA-M57SLI-S4. Tested with Windows Vista SP2 x64 and Windows 7 RC x64 (no change).

I've had several problems with faulty Ultra power supplies before. Here are the stats from my PSU tester:
+5V: 5.1
+12V1: 12.2
+3.3V: 3.3
-12V: 11.9
+12V2: 12.2
5VSB: 5.0
PG: 330ms

Should I sent my motherboard in for an RMA, or could something else be causing this problem?