The beeps you are getting are almost definitely a BIOS beep code. There is a hardware problem and the computer is failing POST. Codes vary by BIOS manufacturer but I think Long-Short-Short-Short usually refers to memory error, or video card error.
Reseat your RAM modules. If you have more then one module, try with just one or the other. If the computer has a discrete video card, reseat that aswell. If that doesn't work, see if you can borrow a video card and plug that into a PCIE slot and test.
If you're still not able to get any output on the monitor with a different computer, perhaps you have 2 separate issues here.I would try to procure a known good monitor, and continue testing with that.