Constantly changing System Preferences and Safari Preferences

It seems like every time I boot up my MacBook Pro (10.6.8), Either/ both my system preferences and my safari preferences have been lost. I expect that this can happen occasionally, but this is truly almost every time. I am the only user on my computer. Surely, this CONSTANT preference losy is wrong; I am losing so much time resettinng things. I have been a Mac user since 1988; this constant problemis something new to me. Please help me find someway to make my preferences stable. Thanks.

Sass