Movies / Videos No Longer Play - Media Player and Installshield Hang Up

I have run into a frustrating problem of late where I can not longer
view movies/videos on my PC and was hoping someone might have some
suggestions. Not only can I not view the videos, but media player
locks up and I have to re-boot whenever I try to use it. The sequence
of events that got me into this a

-My son got an Aiptek IS-DV digital camera for his birthday, so I
installed the some of the software on our PC (PowerDirector and Ulead
photo editor)to try it out. Everything worked fine: could view videos
and view jpgs.

-I went to install the drivers for the camera and was prompted for my
Windows 98 installation disk. When the program said it couldn't find a
file it needed, I made the very dumb mistake of thinking maybe it was
on the Windows 95 installation disk, so I loaded that. Some files
copied, others didn't so I chose ignore. As might be expected, when
the install completed, things did not work properly, so I uninstalled
the drivers.

-At this point, I realized I could not play videos anymore. To
correct, I have tried uninstalling/reinstalling multimedia components
for Windows; reinstalling Windows 98; reinstalling media player;
reinstalling the camera drivers; all without success.

In addition to not being able to use Windows media player, none of my
other media players will work either. Nor can I now install
PowerDirector as installshield hangs during install.

I am running Windows 98SE with Media Player 9 installed. Any
suggestions as to what could be the problem would be appreciated. I
would have thought that reinstalling Windows would have fixed the
problem, but evidently not.

Thanks,
Joe