Vanishing partition. Please help.

I had a 3 year old notebook which was broken in every way possible. So I tried the only sensible thing and took out the 2.5'' hard disc out of the notebook! It is 500 gb big with 5400 rpm. I bought an adapter enclosure so that I can use my hard disc as an external drive.

Here comes the crazy part: After successful assembly...I connected it to my Win 7 maschine and it identified only 250 GB. I am guessing when the notebook broke I had 2 partitions...250+250 GB... and somehow only one of the partition is getting identified.

My obvious question to u guys: Where is my other partition and how do i get it back.

Many thanks in advance.

Pappu