Clear CMOS is simply pressing the button on the board I/O panel or removing all power from the board including taking the battery out for a while.
However, most often missing RAM is from a bad MB slot...have you tested a known good stick in each slot? or from the CPU not making contact in the socket properly, which can be from bad contact...uneven cooler pressure...bent pin. I would reseat the CPU making sure there are no bent pins in the socket and making sure when you replace cooler you do so with even pressure all the way down until it is seated.
Always good to check the seating of the RAM too...these slots are famous for being able to have the latch end closed but the RAM not seated properly....have to hear a good click at each end...non latch end first.
