Vista - default programs --- explorer crashes! and a question about system restore too...

i am using windows vista ultimate and no updates have been installed.
whenever i try opeaning "Associate a file type or protocol with a program"
under default programs in control panel explorer crashes. i try to search
for online solutions but nothing seems to happen. what could be the problem?
in all other ways the system works fine.

also, reently i check the system restore window and i learnt my system has
only 3 restore points. the last time i used my system was on 14th jan and
that was the last system restore point created. i installed vista last
december so i was expecting some more restore points. i have not manually
deleted any and have also not disabled system point at any time. can anyone
comment on it?

thanks in advance.
Neerav