There are a lot of things in a PC or laptop that can cause it not to power up and diagnosis requires a systematic approach to eliminate all options except the correct one. Firstly you must make sure that the computer is plugged in and switched on at both the wall and in the case of desktops from the back of the computer as well. You should also try connecting the computer with a different power cable and socket that you know to be working with another device.
If these don’t work then it is likely you have a more serious problem and we can help with that. A major component may have failed like the computer’s PSU or motherboard. Whatever the case is we can diagnose the fault and give you the appropriate replacement options that will match your price range and performance requirements.