Please try the following steps:
1. From the desktop, click the Start button and select Shut Down.
2. Select "Restart in MS-DOS mode" and click Yes. This will restart the system without running Windows.
3. When you are at a DOS prompt type CD \WINDOWS and press Enter.
4. At the C:\WINDOWS prompt type ATTRIB *.* -H and press Enter.
5. When you return to a C:\WINDOWS prompt, type CD SYSTEM and press Enter.
6. At the C:\WINDOWS\SYSTEM prompt you should again type ATTRIB *.* -H and press Enter.
7. Next, type EXIT and press Enter, and the system will restart and return to Windows.
8. Double-click the My Computer icon on the desktop.
9. Right-mouse click the icon for your CD-ROM drive, and select Install Quicktime from the list of options that appears.
10. After installing Quicktime, you should be able to play Riven