Macros disappearing

Good morning, I'm have a relatively frequent issue with my Excel macros disappearing; I'll open Excel, and under the Tools>Macros where I normally see my list a dozen macros, it's blank. Once I restart my PC, the macros re-appear. The issue doesn't seem to be tied to my use of them; in fact, I can never pin down exactly what I'm doing when they DO disappear simply because it is so seemingly random; I can go days without it happening, and soemtimes it happens several times a day. Anyone able to tell me why this happens and or how to correct it? Thanks!

Sorry, I'm using Excel 2003 and my macros save to the PERSONAL.xls file by default when I save them for use in any Excel file..