QuickTime movies freeze mac, also can't change screen res

I've had this problem for a while now and haven't been able to figure out
how to correct it.

QuickTime often freezes my system when trying to play movies. I have
reinstalled QuickTime and reinstalled my whole system with no change.

Attempting to play a working movie (not all freeze the system) and switching
to full screen will freeze, as will just trying to resize the window.

Also happening is I cannot change the monitor resolution without getting
a blank screen and system freeze.

G3 266 448mb, OS 9.1, QT 6.0.3. I am using a Belkin converter to connect
to the ViewSonic monitor (which worked fine for a couple years without
this problem). Using the seperate Monitors CP and Sound CP.

Any ideas or suggestions greatly appreciated.!