fware offers solid suggestions. With the PC software, you can even populate a blank SD card with a minimal boot environment for testing purposes. Sort of a "safe mode" that won't include your existing vehicle profiles if your update contract has completed with the 12 months.
The good news is that if you're getting as far as the menu, that means the boot operating system isn't damaged (first Windows CE boots, then the SD card is polled for, then the MaxiDAS application is loaded off the SD card and the vehicle profiles are populated through the buttons on the left based on what's installed).
Definitely try a new SD card. You can use almost any modern computer to copy the contents over from your old card. Whatever you do, don't delete anything from the old card.
-Jeff