Here are some things you can try:
1) Run a virus and a malware scan on your windows 7 machine
2) Uninstall knight online, then do the following:
- run a disk defrag on your hard disk(s). You can use the Windows 7 disk defrag utiility, I personally use the free one provided by auslogics, it's faster and does a better job.
- After the disk defrag has completed, reboot and reinstall knight online
3) Goto the windows system event logs and look for any errors that may have been logged while starting knight online. Report errors if you see any....
4) Make sure your graphics card drivers are up to date