How to Run chkdsk on a disk without a drive letter

Open a command prompt.

Execute the mountvol command which will tell you all the volumes on your system and give you the GUID of them.
\\?\Volume{eb38d03b-29ed-11e2-be65-806e6f6e6963}\
*** NO MOUNT POINTS ***

\\?\Volume{eb38d03c-29ed-11e2-be65-806e6f6e6963}\
C:\

\\?\Volume{41ae7a1c-9849-11e2-be7a-0026b9dc157c}\
F:\

Windows will give the GUID if it’s has valid and recognized partition.

Then run CHKDSK in this fashion:

chkdsk “\\?\Volume{eb38d03c-29ed-11e2-be65-806e6f6e6963}”

Use /f and other switches as appropriate.