What do long continuous beeps (with a pause in between, each beep approx. 3s, repeated ad infinitum) error code mean at startup of a PC?

Other symptoms are: no image at the monitor at all.

The solution ideas here are by priority of what to check.

1. It might mean defective RAM, or defective video RAM, or incompatible RAM modules or incompatibel video card. See its05.de: BIOS Fehlermeldung.
2. On an Award BIOS, it might mean: graphics card not inserted properly. See this hothardware.com thread.
3. It can also be a warning of a temperature, fan or voltage problem. Hence it might indicate also a power supply unit failure. See this computing.net answer.
4. It can also mean CPU or motherboard failure. See this computing.net answer and this computerhilfen.de article and this pcwelt.de thread.
5. Further option: so-called “full reset”. See this pcwelt.de forum post.