Why does electricity turn on and off in one part of my house?
If you can find a breaker that controls all the same lights and outlets this would be helpful. If it is just 1 breaker most likely it is a bad hot connection. usually in a junction box at an outlet or light switch but it could be the hot wire that connects to the breaker, very unusual for a breaker to do this but it could be the problem also. Find the breaker and see if some areas turn off that were on when the power goes away that will help narrow down where the problem is.
It could be the neutral wire also but I have less problems with these and am not sure why as they normally carry the same current. If you find 1 breaker and additional lights or outlets turn off when you turn the breaker off go to the last working outlet and check the connections there (with the power off) if those are good go to the first non working outlet and check there.
If everything is the same when turning the breaker off as the power fail, you will need to remove the dead face of the breaker panel and verify the wire on the breaker is tight, follow the wire back to where it enters the box with a white wire and follow that to the neutral buss and make sure that is tight.
the last thing would be to try and replace the breaker looking at the tab to make sure it has not arced and burned the tab the breaker connects to.