Try this:
PC Software for K810 (from sonymobile.com)
If you still can't access your files via software try opening it in Windows Explorer (if it's recognized it'll be in My Computer).
Alternatively boot a different operating system live CD and try opening it from it. I've got an old MP3 I couldn't open on Windows (wasn't recognized) and could open it on Fedora (just open to get the files, there wasn't any software available, though). Or just try on a different computer...
Edit: I remember I also had an old webcam with no drivers for Windows 7, just XP, so I installed it on a virtual machine and it worked - since it's an old cellphone you could try that if nothing works...