It's basically in the title.
I've been using the 32bit edition for a while now, and decided to give the 64bit edition a try. It was fine when using the live DVD session, but when I log into the installed system, the CPU usage just flies up to 100% on all cores and the system freezes within moments.
I'm using an Asus M55S, the CPU is an Intel Core i7-2670 QM at 2.2 GHz.
Like I said, the live session worked perfectly and windows works on 64bit so my CPU definitely supports it. Any ideas?