Umm, where did you get shift from. It's just like I typed. Think about doing Ctrl-Alt-Del, this is the same only with first Alt-SysRq-s then release all and do the same with u, release again and then b instead of s or u. You can wait a few seconds between the commands, especially if you notice the hd spinning while syncing. If the computer is really so frozen that this doesn't help, I suppose a cold boot with the power button is the only option, but cold booting should also be the last option you try.

You could wade through /var/log and see if something of interest can be found in messages, XFree86.0.log or syslog.