Photoshop CS5 freezes

Hi,

Have been using PS CS5 since the trial became available. But seems CS5 responds a lot slower than CS4. Sometimes, it just freezes or slow the whole computer down when I tried to open a many-layer file. I had to force quit the application, It's really frustrated because the system responds very slow even I tried to quit PS. Once it's quite, everyting's back to normal. Does anyone have this problem?

Thanks,