Tried booting up with my old hard-drive (which booted up fine less than a few days ago), which then gave me the error of "Invalid Partition Table."

I have no recent backup of all my personal documents and school files meaning that I'd be left stranded with a stupid partitioned hard-drive that doesn't work.

So, how can I recover from an Invalid Partition Table? Any tools that would help me? I only need to get data from 1 of the 3 partitions. And the data on there is minimal. Probably less than a gig.
-- mrcodedude