The home button stopped working
I followed step-by-step ifixtit.com guide and video. If this is the first time you are repairing an iPhone 4, it will take you a while to familiarize yourself with the components, screws, etc. Make sure you take your time to do it right and find a good method to keep track of all those screws. Personally I printed the IFixIt.com sheet and I just placed the screws on top of that sheet as I was dissassembling the iPhone. IMPORTANT ADVICE: Be very very careful in the last step when you are removing the screen/digitizer. I damaged mine and had to order another one. Do not apply too much pressure to the screen and, if you can, use a hair dryer to dissolve some of the adhesive before you try to remove it.
1. Be patient and make sure you have enough time to do this properly.
2. Do not apply too much pressure to the screen when removing it
3. Be very careful when you are re-inserting the screen back into the case. As the guide says, both cables attached to the screen SHOULD be the same length after it's been assembled. If not, then one of the cables is probably blended and you may have damaged it.