I have a partioned hdd...was disk c &e... c for opsystem and e for data..after installing new op system the other partion has become unallocated is there any way of fixing this
Yes! In order to get back your data, you could run some data recovery software to re-access your data and then restore the unallocated space by creating a new partition. (There are many data recovery tools available online. You should pay much attention to this thing.)
After experiencing this trouble, you also are supposed to back up all your important data regularly.