"1., How can I get back my data that was strored on /dev/hda6 mounted as /home
2., What could be the reason for this to happen
3., Would it be a good idea to put / o /boot in other than reiser fs"
This problem could have one of several causes. Here are the possibilities and the fixes:
A. You could have filesystem errors, perhaps caused by improper shutdown. So the first thing to try is to boot a rescue CD and run fsck against every Linux partition except swap. It is important to give fsck the correct filesystem type. Assuming that you are using reiserfs then the commands would look like:
fsck -t reiserfs /dev/hda1
fsck -t reiserfs /dev/hda2
and so on. Answer y to every question that fsck asks.
B. If A. doesn't work then you may have hardware problems with your IDE controller chipset. Swap your hard drive to another computer (Let's assume that your drive is now /dev/hdd on the second computer). Boot your rescue CD and try mounting /dev/hdd6 to retrieve /home.
mount -t reiserfs /dev/hdd6 /prayer
ls -l /prayer
If you can access /home this way then copy /home to someplace safe on the second computer.
C. If you still get hardware errors after running fsck and swapping to a different computer then you probably have a broken hard drive and you are probably screwed.
Be prepared. Create a LifeBoat CD.