I suspect you have other problems. Freezing your computer isn't likely to be a Photoshop issue, and if your computer won't boot now, that's DEFINITELY not a Photoshop issue. Something else is wrong.
When you connected with target disk mode, did you run Disk Utility to repair the disk? The most plausible explanation for your symptoms is that you had disk directory corruption that's been eating away at your computer for a while now, and Photoshop made the problem worse. (Because it does lots of disk writes and creates and deletes huge virtual memory files, Photoshop is twenty shades of living hell on a disk that has a damaged directory. If your directory is corrupt and you use Photoshop a lot, the corruption will tend to get a lot worse, really fast.)
So while you may have started seeing the problem when you used Photoshop, I would say that it is most likely the actual SOURCE of the problem is somewhere else. I'd recommend scanning the disk with Disk Utility, and if that finds and fixes problems but you still can't boot, re-install OS X. You should be able to do this without losing data.
