If an LG flip phone is not working properly, a series of diagnostics are necessary. Issues vary from physical damage to connectivity issues, firmware problems and service issues. Full documentation for a specific LG flip phone model is available on LG.com
To troubleshoot the problem, first check if the phone turns on. If it doesn't, make sure the battery is in place and seated properly. If it is, replace the battery. If the phone turns on, but the screen is blank, it's possible that the screen, logic board or hinge are physically damaged. Similarly, if the phone turns on but doesn't function properly, a firmware problem is sometimes to blame.
Frozen phones often just need a full reset. To do this, turn the phone over and remove the case from the battery compartment. Lift the battery out fully, and wait several seconds for any latent charge to leave the phone. Then reinsert the battery, and close the case. Restart the phone as you normally would.
If you can't hear the person you're talking to on the phone or he can't hear you, there is likely an issue with the speaker or microphone. Likewise, if the speaker phone function does not work, there is probably an issue with the external speaker. If the keypad does not function, check for obstructions under the keys and make sure the keypad is not misaligned on the phone.
If the phone seems to be working properly, but you cannot make a call after confirming a signal, there is probably an issue with the service. Call your service provider to make sure that service is active.