Do you have problems with only the PAL games? or games from both regions?
If only PAL games, then make sure you set the video display options for those games to "Force NTSC" in whatever USB Loader you are using.
If you are having problems with both games, post a syscheck so we can see if your mod is current or not. Directions on how to generate and post a syscheck are linked in my signature. Post the syscheck as a reply to this thread.