If the previous user upgraded, the RTC clock problem (very old firmware problem) will not occur, although I guess the clock battery could fall out (any rattle?), but this will not brick the XO.
Since you see the microphone light flash, it suggests that the software may have may have become corrupted during shipping. There were some such problems during last G1G1 (during winter).
Suggest you try doing a clean install from USB drive:http://wiki.laptop.org/go/No-fail_upgrade
Very simple if you have a access to PC or Mac on internet to download the images to a USB drive.
Then put drive in XO and hold down all four game keys (under right speaker) while powering on.