Thanks for the help guys, it was the missing PRAM battery. Unfortunately after succesfully booted my Mac (with single gong), i went to eat, and when i came back, my 540MB HDD died

One last issue: A just replaced the HDD with the one in my LC, and MacsBug 6.5.3 isn't loaded in my Overclocked LC III. (As i didn't tested it before OC, i don't know if this case is related to the LC III itself, or the OC caused it). (System 7.5.3)