These 4 beeps that you hear mean that there is a failure with the system timer. It afects the POST /Power On Self Test /. It is a set of procedures that a computer runs through every time you switch it on. It ensures that all of the system's hardware's working properly to ensure the loading of the OS. If the computer does not pass POST, it won't boot.
Have you added new hardware recently? If any new hardware has been added, please remove that to check if it is the cause of the problem. If your computer works after removing the new hardware, it can mean a few things. Either the new hardware is not compatible with your computer, a system setting needs to be changed, or the new hardware could be defective.