I doubt it had anything to do with the update. If the error appeared 2 days after the update. Where were the additional drive letters? On the same HD? A second one? Or maybe network folders?
If it was on the same HD - although it doesn't sound/look like it - it must be one of the three partitions/volumes behind the C-Drive. To mount the partition and assign a drive letter you can:
- Right-click the volume
- Click Change Drive Letter
- Click the Add button.
- Choose from a list of available drive letters. (You might not want to use A or B, which have historically been reserved for floppy drives and can sometimes confuse older software.)
- Click OK
If you have two Harddisks and one of them disappears during operations and only comes back after several reboots you should make a backup, either the Harddisk or s.th. on the mainboard (HD controller etc.) seems to be faulty.