Did it always give a single beep when working properly??
Your substitutions sure make it sound like an unusual problem. Bad CPU, memory should give beeps, also bad video [which you eliminated well]. Only other guess is Power Supply, with no good reason.
Could be bad BIOS or battery, but your "seems to boot OK" kills that idea.
This problem is a lulu. Be sure to let us know what the problem was when you solve it.
I have a Blaster Pc by empac and all of a sudden I have no monitor signal. I tried a known good monitor and still nothing. Next I bought a new agp video card and still nothing.
I swapped it out for a pci video card and still nada.
Is this a motherboard problem.
The computer seems to boot up ok with no error beeps but I'm not sure what to do next.
TIA for any help.