lost files after update..

There is this: http://journalxtra.com/linux/desktop-recovery/the-definitive-guide-to-getting-your-linux-desktop-back/

It's a bit long winded, but it's worth looking at. Perhaps you should start from the Partition that works and "Solution Two".

When you say it won't reboot, what happens, what do you see?

It may be my imagination but this problem seems to be happening a noticeable bit at the moment e.g. http://forums.debian.net/viewtopic.php?f=5&t=121269

If all else fails you may have to rescue your files and do a new, clean install. http://www.alandmoore.com/blog/2012/02/03/recovering-data-from-a-pc-a-guide-for-not-computer-people/#more-273

When you get the Purple Screen can you Ctrl+Alt+F1 to get to the Terminal Screen , and try to update from there?

One thought is that you might have a video driver installed. Sometimes when you upgrade to a new kernel you have to re-install the video driver.

I hope that you recover all files, because with a recovery software it will not be easy and you can have a corrupted files