Machina

My HDD is in fine physical condition. What happened was my MBR got overwritten by a Slax Live CD and I suspect one of the MBR recovery programs I ran modified the partition information of my hard disk, and now Windows only detects the first partition on the drive which is supposed to have a total of 3 partitions. The remaining 300GB is shown as unallocated. I have copious amounts of critical data in that space. Does anyone have any suggestions on restoring the remaining two partitions?