The mission team at least has a possible culprit: it believes that the receivers and transmitters have been damaged. Since Philae is hooked on to the comet in a dangerous position, it might have been covered in too much dust to work properly.

If nothing happens by the end of January, that's probably all she wrote for Philae. The comet will be far enough from the Sun by that point that it'll likely be too cold for Philae to operate at all. At best, researchers will get a close-up look at the vehicle when Rosetta winds down its mission in September. Don't weep too much for the apparent loss, however. Philae did send some important findings to Earth, including the comet's internal structure and temperature shifts. The operation wasn't a complete bust -- it just fell short of the (fairly lofty) expectations.

[Image credit: ESA/ATG medialab]