Good vendors for replacement alarm panel/keypads?

I sell alarm system components to DIYers so I recommend my store, but I'm a bit biased in that regard. :^)

There's no "rocket science" to installing most alarms. If the wires and sensors are already in place it'll be a piece of cake for a talented DIYer. Depending on the brand, one part that can sometimes be a pain is programming. Ademco's Vista series are fairly easy to program directly from the keypad. DSC is also easy but Ademco is better built. Napco Gemini models are more complicated to program but they are also the most configurable alarm panels on the market.

If your friend wants home automation as well as security, you should consider Napco's P9600 or even ELK Products' M1 Gold (higher cost but awesome power).

Sounds to me like some wires have come loose. Check the connections at the keypad and at the control. On some 22/4 station "Z" wire, the wire can actually break insided the insulator. It looks like it's a solid wire but when you start bending it a little you'll notice the break. If all the terminals are tight and it looks like the wires intact, then it's time to check out the actual wiring before you start replacing components.