If it is a continuous beeping sound, it is most likely a failed or failing video card. You don’t say if you have an on-board video card or not. You have several options here with this issue. You can attempt to place a new non-on-board video card in the slot or slots on the system board and see if you get a video signal then to the monitor. If that fixes the loss no video signal problem, then you can turn off the on-board video card via the bios. If placing a new video card in the system is not an option, then you will most likely have to replace the system board in your PC.