Service Pack 2 Update Problems

I installed xp service pack 2 through the automatic update and restarted the
system. After that, every time when I start the windows explorer, it will
take a while (several minutes) for the windows explorer to locate the files
and folders under c: drive. Once, it found and displayed all the files and
folds, everything looks fine.
Also, when trying to change the file directory in "Look in:" drop down list
on the "file open" window of all the programs, the program will get stuck
there for a while. In the mean time, the system seems doing nothing but
thinking. Such problem happens for all the program and all the time. Thanks
for any help!