Question : Problem: No display seen after a while. when rebooting no display seen. when disconnected after couple of hours and reconnected the display comes on subsequent reboots the display doesn't come

I have bought a used motherboard and processor  from ebay.
when i checked it with RAM, VGA Monitor and Keyboard for the POST. everything was ok. Got the single beep.
But when i connected motherboard to the chassis(assembled) of the computer and tested again.
It booted. when i disconnected added another 128MB RAM.. the display came up. when i booted again after connecting the Hard disk the harddislk got recognized but i heard a 'clank' sound. Then when i rebooted again.No display seen. No single beep. when i inserted a debug card and removed hardisk,memory of 128mb still no display seen.

Debug card always shows -l POST Success and  FF result which is Mother Board Ok.
when rebooting no display seen. when disconnected after couple of hours and reconnected the display comes on subsequent reboots the display doesn't come.

Tried BIOS Jumper reset clearing ... CMOS Battery reset and all.

This is confusing .. Not able to Pin point the issue .. whether it is Processor or Mother Bard or RAM ... VGA etc.? can anyone help ...

Answer : Problem: No display seen after a while. when rebooting no display seen. when disconnected after couple of hours and reconnected the display comes on subsequent reboots the display doesn't come

I have seen symptoms like this twice.
The first was when the PSU I was using was not powerful enough for all the components I had installed. I found that removing some components would allow the system to boot and display, presumably because there was more power available for the VGA card. A new higher powered PSU resolved the symptoms.

The second time was also PSU related. This time it seems the PSU was slowly failing. Eventually the PSU stopped working at all, and once replaced I didn't get the symptoms again.