I searched your symptoms on google and found this:-
"NOTE: Before making any attempt to remove or replace any part inside the casing, ensure that the power is off.
Well, the first thing that might be causing this is your memory card (RAM). Try to remove it and place it in another memory slot on the motherboard.
To be sure if your motherboard is still in good working condition, remove the memory card and power on the PC.
You should hear continuous beep sounds.
If you hear this then your motherboard is fine.
If placing the memory card in another slot does not work then the problem lies with the memory card itself. You will need to replace it.
It could also be that some faulting PCI cards are causing this error.
Try to remove your PCI cards. Normally a faulting PCI modem causes this type of error. Remove it and then power on the pc."
It may be worth having a look. I seem to remember having a similar issue years ago with an old PC and it may have been the PSU loosing a rail so my PC wasn't getting enough juice to boot up.