Update on MHDD32 solution
I had the problem of 1 TB Seagate Drive showing up as 33 MB on two different drives, and have no idea what caused the problem, but both had valuable data which caused me near heart failure when I could no longer see my drives (and partitons) any longer. After much searching on the web, I found the MHDD32 solution using the Ultimate Boot CD which worked successfully, and as a further bonus, lost absolutely none of my data after running the process. What a relief at being able to sleep peacefully that night. This is the solution which worked for me:
Download the Ultimate Boot CD ISO file (I used version 5.0.3) and burn it to a CD
Boot the CD
Select 'HDD'
Select 'Diagnosis'
Select the application 'MHDD32' (I used the V4.6 version)
Select '2. Start the computer without SCSI support.'
Reply to the "Enter HDD number" prompt. In my case it was 6
Type the command 'NHPA' (the description of this using the 'Help' command is 'Uncut (return to factory size)')
Reply 'y' to the "Do you want to set Native LBA address ? (y/N)" prompt
Reply 'y' to the "continue? (y/N)" prompt
The reply to this is "Done."
I did not need to do anything further and my drive was restored to its original state of being a 1 TB drive
and all the data on it fully preserved and accessable once again. What a relief !