HDD partition show unknown help please?

Hello guys I need help my HDD partition show unknown. I had a Desktop PC with 80GB HDD and Windows XP Pro. I purchased a new Desktop with Window 7 Operating System and disconnect the HDD from my old PC and connect with new Pc via IDE cable. Now problem is the HDD shows unknown partition and I cannot noting but delete partition. Please help I did not take backup and need all these data back.
