Profile Wiped

I had this strange problem where I was trying to access a samba share who's folder was not created cause my entire windows xp system to be practically freeze to a point where I had to reboot.

However on reboot I noticed the two portable apps firefox/thunderbird which was running at the time had their complete profile wiped clean! Lost all account information in thunderbird and firefox lost all passwords...

Luckily I had a backup over 2 months ago but anyone know how this happened and what's the proper way to prevent this from happening.