Somebody touched my computer !!

i turned on my pc today and noticed that it looked like somebody had reinstalled internet explorer or maybe restored my comuter to an earlier state.some kind of a restore action was made for sure bacause i changed somrthing in the win.ini this morning and now it has changed back to the original value.
i know my brother and his friend used the computer today but they didn't say enything to me...they should have !!
Anyway, how can i tell was was done ? is there a log file in which i can read what happened ??? there has to be some kind of an answer !!
thanks in advance !!

If the change was done by someone using the restore function, the very least you'll be able to do is go into the restore wizard [as if you were going to set a manual restore point] and look at date and time of last restore. If it's out of sync with regularly scheduled checkpoints, you'll have your answer. If it is, go for "undo last restore," or restore to a point after you edited your win.ini file. LOL, I hate when the machine gets messed with!