The Mechanics of a remote control - repairing 
Consumable.
I would consider remote controls to be consumable, like car tyres that wear out and the amount of wear is obviously connected to the amount they are used. Nevertheless, you want to watch the world cup tonight and get the projector setup so wish to fix your remote.
As you press the buttons oil leaks out of the pad. When you open many remotes, you may see some rather disgusting gunk. This can be water, juice and sweat that has eked its way in, but might be from the pad. It can be cleaned off. So too can the PCB, but be careful not to take any black contact track off. The keypad carbon will degrade making the most commonly used button inoperable. Only a new keypad will fix that properly.
The first check would be the battery contacts. Any rust can be removed using a file or similar implement.
Getting the remote open is often the biggest challenge, quite difficult in some cases to open without causing even more damage. I use an artist's pallet knife and carefully prise it open bit by bit.
Inspect the LED, sometimes a dry joint is easily spotted. Wiggle to see if loose. Many people will re-solder, but in doing so break the PCB track. If so, just run a link wire to somewhere further down the board.
Swap the crystal - make sure it one of the same value.
Check the voltage going to the LED. You normally get a 1.5 volt drop across it.
Aside from that you will notice that there is not a lot inside a remote. It is all about the software in the chip.