Reinstallation would be your call. As far as what distro to install, again, that's your call. Everybody has their personal favorite(s), but that doesn't translate to what's best for you. Check out http://distrowatch.com/ to find out more about specific distros.

How to troubleshoot your problem and avoid a reinstall? Well, it's going to start getting difficult. Based on the fact that you've successfully gained access to your data via Knoppix and Windows, but can't boot, I'd start leaning towards troubleshooting a bootloader problem. Or some disk/filesystem error that is affecting your bootloader (maybe a corrupted config file - "menu.lst" for Grub). Can't say for sure that this is your problem, but that's one of the first directions I'd start investigating. Also, I'd look into running fsck on your partitions (from a Knoppix boot). Maybe even a low-level harddisk diagnostic tool supplied by your disk's manufacturer (e.g., Seagate provides something named "SeaTools", I'm sure other manufacturers have similar diagnostic tools available). These initial troubleshooting steps amount to taking a shot in the dark. They will either turn up something, or help you rule something out.

You are probably using LILO or Grub as your bootloader. I don't know which Mandriva uses by default, but for some reason I'm suspecting LILO.

Hi Haertig,

I guess I took the easiest way out and made a fresh installation :P. I'm currently trying Ubuntu. It seems good, but still checking.
One important thing for whomever is reading this thread, DO NOT rely on Explore2fs for copying data from Linux to windows. In my case it copied all the email files but with a file size of 0 so be careful there. I almost lost all my emails. Which reminds me, THANKS A LOT Heartig, the commands you gave me to burn the data to DVD worked perfectly.

Now I am stuck with another issue (emails import/export). But I guess it should go fir another thread.

Regards
Linuxlainen