Found the issue causing the problem.
I tried the various solutions that have been mentioned but nothing seemed to work BUT i installed the partition wizard software (
http://www.partitionwizard.com/download.html) & when i viewed the disks within the PW, i could see the missing partition and i could explore the files.
Now, for some reason, the partition had been set as a hidden partition (i'm not sure where this setting can be set). Within partition wizard i was able to unhide the partition.
I could then go to windows 7 disk management & was able to assign the drive letter to the partition and the drive is working & my files are still on it.
Thanks for all your help guys.
Regards, Shuja