This is a weird problem. I know three GS3.1 users who have had this happen.
GS3.1 quits or hangs (both have had the same result). After re-booting you go back to the file you were working on and it now has no data in it, showing 16k in the file size. Before the crash, your saved verion had 3500kb+ of data, so something in the crash wipes the project file clean.
I have also had this happen following a gigantic midi burst and hang, but it can be prompted by a crash on save as well.
Anyone experience this? I'm running GS3.10 on a dedicated 3.04Ghz system, 2gig ram, XP.