RE SETTING CMOS

Hi Thanks for swift replies
I have removed and replaced battery with new one I have also shorted the jumper pins on the motherboard to reset CMOS. As I said originally I have an Identical computer? I too thought of the power supply so I swapped them over and problem still persists. Just one thing sometimes when I switch on pc you can here it going through normal routine to boot up but no screen and sometimes switching it off and on wont work if I rock the pc case from side to side as hard as I dare, there is a click inside the pc and the screen then activates I have tried to do this with covers off but impossible to see or hear cause. I too thought motherboard?
I have looked online for a replacement board but to date have not found one for socket 370 for intel p3 coppermine I am loathed to give up as even though its an old PC its still faster than most