SJ wrote...
I know it sounds ridiculous, but because it happend couple of times,
i wonder if it's happening to anyone else.
1. Some formulars in cells changed randomly. For example, if the
original formular was "=d5/d7", it changed to "=d6/d8" even though i
haven't inserted any rows or columns.
2. Numbers changed randomly. If the number was "30", it changed to
"0" couple of times.

Did anybody have similar experience?

This could be a hardware problem rather than software. Flaky RAM could
produce such behavior. You may want to run memory diagnostics.