where is my files !

the problem is simple
when ever i restart my computer every thing i did in that computer is reset for example if i downloaded some files it will be gone
if i changed my administrator password it will be reseted the way it was
also including registry settings windows updates every thing

the strange thing is everything is normal the anti-virus detects nothing, every executable running is safe , all dlls loaded are safe nothing seems to be wrong and there is no rootkits

any ideas?