Do you mean it freezes when you are in the vsh, or when you are playing the iso?
If the select button in the vsh works, open it and set the driver to m33-driver.
If it still not work, restart the psp, reload ChickHEN and Gen-a and try the iso again.
And then if it still not work, install CFWenabler and try it with this.
If it still not work, the iso is not compatible.
If the select button in the vsh not work, install CFWenabler and when it