probably the rom ur trying to use (it's happened to me a few times)
or ur computer (make sure it can handle the games)
also try different plugins and check tha configuration of them
it should cause i play games like warcraft 3 and guild wars the games that keep on freazing are harvest moon 64 and orgre battle 64 and my emulater is project 64
well, as I said before trying d/loading a different version of the rom(s)
it's happened 2 me before with a couple roms where they didn't work, and when I d/loaded a different version, it worked perfectly...
It might not be the roms if it is happening often. Also, even if you CAN play modern games on your pc, doesn't mean it will run 64. I would recomend you check your settings. Particularly with the 3D plugin.