It's possible that you have a previous version of Flash installed, and the
newer version needed by some web sites has a problem installing over the
older version. I had a similar problem. The fix was going to the
Macromedia site, and downloading the FLASH PLAYER UNINSTALLER FOR WINDOWS
for the previous version, executing it, rebooting, then downloading and
installing the latest version of Flash Player for Windows at the Macromedia
site.
For the Flash Player Uninstaller for Windows go to:
http://www.macromedia.com/support/flash/ts/documents/playerfaq.htm
Scroll down to: How to Remove Flash Player From Your Computer. Download and
then double click to execute the Flash Player Uninstaller for Windows.
There are two versions of the Flash Player Uninstaller for Windows, one for
Flash Player 6, and one for Flash Player 7. Try using the one for version 6
first. Then when Flash Player is removed, reboot, then go to:
http://www.macromedia.com/
and download and install Flash Player 7. If that doesn't work, download the
Flash Player Uninstaller for version 7, and do the same as above. (perhaps
you already had version 7, and it was corrupted). Make sure to reboot after
uninstalling, and then install the new version.
If the above isn't applicable go to:
http://www.macromedia.com/support/flash/ts/documents/playerfaq.htm
and scroll down to: Troubleshooting and see if you can find the answer by
clicking some of the links there.