Laura,
I volunteer for OLPC.
It is likely that your XO lost charge on its internal battery which
now prevents the display from functioning.
Here's some details on the 'fix clock' issue, see:
http://wiki.laptop.org/go/Fix_Clock
There are volunteer repair centers that can more fully assess and
repair your XO for nominal charges and you pay shipping, see:
http://wiki.laptop.org/go/Directory_of_repair_centers
I have a serial adapter for this repair and perhaps I can help.
Sandy
--
Mr. Sandy Culver
http://wiki.laptop.org/go/User:Culseg