you could also try downloading a free partition software such as Minitools Partition Wizard v9 - it will bring up an interface much like the windows one - try right clicking on the partition and assigning a letter.
Might work, and if so save you starting from scratch, if not, then at least you know its not just the windows disk manager.
You could also then try recovering the partition from Minitools, using the partition recovery wizard - again itmight work and you can get the whole partition back - and you may be able to browse the results and see the files you need to recover.
Then you can decide whether to try recovery software. Both EASUS and Minitools do very similar Partition and Recovery software, and the free versions are pretty useful before it starts to cost. I used EASUS today and it let me save an xml of the partition status after the scan, which was very useful as the scan took about 8 hours and I didnt want to lose it and start again if the power went out!