Seeing as how this is an older device, first thing you should do is confirm you have the latest firmware.
The next time it happens, go to Start->Run, type "cmd" (no quotes), and hit enter. In the command window, type "ipconfig /all > temp.txt" (no quotes) and post the file's contents here.
Once it returns to normal, generate a second ipconfig dump and post it as well.
I want to see if something happens to your TCP/IP configuration during these outages.