Has the pc been moved around recently? Have you had electricity problems going on (storms/spikes/etc) ? These are things that could possibly effect the connections and the circuitry itself which is what the bios tests for the minimum it needs to turn the big box of wires into a working computer.
BIOS manufacturer's website will tell you exactly what the the beeps mean. Bios is first thing you see on the screen as you switch it on. Be quick and don't blink or you'll miss seeing it. You need the manufacturer and the version.
Simple things to check are keyboard / mouse plugged in the wrong way round. I'm forever doing that one.
Hard drive, Video, Network, Sound, LPT Printer are not tested by post unless the connectors are physically gone. These are tested later.
Next check connections inside are firmly in place. Don't be too rough in there while your checking.
Next step, memory. (happens surprisingly a lot in this day and age even on fresh out of the box equipment)
If it's anything to do with individual parts of you motherboard then it's usually a lot cheaper and more straightforward just to go out and buy a new one.
