Xubuntu Installation Error

Hi,
First, I tried installing Xubuntu without deleting Gmac, but it gave an error, so I restarted.
I'm trying to install Xubuntu with my USB. But it gives an error, "gfxboot.c32". I'm writing 'live' to command line, it's solving. But it gives an error too, "Keel panic-not sycning". How can I solve this problem? It gives this error in Gmac too, but i can solve it with recovery mode.(My English isn't good, sorry.)