I use a utilitity called Bitser for this, you can download it from www.bitser.org, and it is very easy to use for checking hash sums in the Windows environment
Download and install Bitser. Copy and paste the checksum you got with the ISO into any text editor, anything from Notepad to Word, then RIGHT click on the ISO file in File Explorer and in the pop-up menu you should see 'Bitser'. Click on this and another little menu pops up, scroll down to the entry 'Checksum', click on this and select the type you want to check. After a moment or two a checksum will appear, copy this and paste it into the same text editor under the first one. You can then easily do a visual check to ensure that the two are identical.
If the disc you have the ISO on is 'closed' then it will show 0 free space. Windows assigns drive letters not quite at random - the OS is always on 'C' - but if you had a USB drive of any sort in this might have pushed your DVD drive down to 'E' from 'D'.
Just a note. If this DVD has the Mint ISO on it you will not be able to use it to install, the ISO needs to be 'unpacked' in some sense before you can use it as an installer. Everybody tells me you can do this directly from file Explorer but I have never managed it ! I was advised to try a very simple utitlity called BurnCDCC from www.terabyteunlimited.com. All this product does is take an ISO file and turn it into an installable disc and as it is just an .EXE file, you don't even install it.