Faulty home button or ribbon cable
I have been using my iPhone with a faulty home button or ribbon cable for so long I can't remember. It came to the point a month ago where the button didn't work at all. So I had to assign the optional assistive touch button to access or close apps and that drove me insane. Enough is enough I finally threw in the towel and got online to see if there was a fix and sure enough iFixit popped up. I thought why the !&&* not. The video and step by step guide seemed simple enough and they even had the right tools. So I placed my order which arrived within a week. Not too bad. Following the video and step by step guide as I thought was easy enough and though the screws were so tiny having the right tools for the job made things quite easy. The only thing I think I did wrong was apply to much force when lifting the front panel off the backing case with the suction cup which came right off without needing to pry the two apart with the tools. Luckily I didn't damage anything. I replaced both the ribbon cable and the button as I wasn't sure which was faulty. Putting things back was fairly simple as well and my phone powered up without any issues. Freakin awesome. Thank you iFixit I am so happy.
My advice is don't wait too long to fix your device. I had to use the assistive touch button for so long that now even though with the new home button in place, out of habit I still look for that damned assistive touch button.
iPhone 5 Home Button Ribbon Cable
Phillips #00 Screwdriver
Small Suction Cup
P2 Pentalobe Screwdriver iPhone