The first thing I would do is if it is working fine is make a software backup, and save to on a clean windows PC. Do not let the DS708 WIFI connect to internet. Next I would buy a new 16gb class 10 Sandisk SD card and format it in FAT32. Copy and paste the backup software saved on your PC on to the new formatted 16GB Sandisk SD card, eject it and see if it works in the DS708 and put the original SD card in a safe place . Install the DS708 software suite CD on your PC . Retrieve the DS708 serial number and register password by clicking Setup/ Help , then click on box that says "About" and write everything down. Go to Autel website and register the tool. If the tool still can be registered and updated , use the DS708 Software suite on your PC to update the software on the 16GB card in the USB card reader ,one car make at a time. What ever updates that are available now are likely the final versions of car make software  the DS708 is ever going to see. 

 Hi witsend, its almost same issue with me, one of my friend purchased it and never got it registered, now its sdcard is corrupted, unable to register (as do not have password to do it), not able to use it. will be very much thankful to you if you can help me out how to restore files on the new card or so. pls help. Thanks.  

 I'm not sure, every serial # and register password is unique and copied software just won't work.All you can do is e-mail support your serial number to see if it's ever been registered before and when. If not, see  if they can look up and give you the unit's register password , register it and send you any dot execute file you may need to copy and paste to a new blank SD card that is formatted in FAT32 in the USB card reader and to be able to  use the DS708 Software suite on your PC to start Downloading  the software to install on the SD card .Good Luck