Can't detect my internal (primary) partition on HD.

Hello and thanks in advance for your time and help!

I own a MacBook Pro which gived from my father in law a few months ago just for a normal use (browsing etc)

My story (issue) is this:

Its HD has 2 partitions, 1 Main HD & 1 Macintosh HD. A night I closed it and went to sleep but the day after it didn't boot up. Tried a few steps CMD+R, OPT+CMD+R, OPT+CMD+P+R etc. While booting via (OPT+)CMD+R at Disk Utility, I can see my main drive and its size but I can't erase, verify or repair it. Only the macintosh.

I did a new installation from CD but I couldn't find my main drive only the macintosh partition, so I installed it at this partition (I did “erase” earlier an this specific partition). When getting into the desktop and I go to Finder or Disk Utility I can't see my main HD at all again.

Any idea how can I get my main partition of my HD working again normally? Because it seems that it works (since I can see it at CMD+R’s Disc Utility) but not inside the fresh installation or while booting normally.

Thanks in advance once again!