Hello!

I'm trying to switch on my PC but it just beeps and nothing is displayed.

Please help me to get it working

Sounds like something is loose in the PC - My guess would be the graphics card. Check all the leads are connected properly. If they are, it will probably be best to take the PC to a computer repair shop. If you were familiar with the insides of a PC you could open up the case yourself and reseat the graphics card. But ONLY do this if you are confident. Tinkering with the insides of a PC can both damage your PC further and you can be seriously injured if you aren't careful.

Stop the external electric supply and remove the battery... put it again and then switch it on