Keyboard not "fully" working after battery replacement.

Hello,

After replacing the battery on my MacBook Pro (Model A1502; early-2015), the trackpad and keyboard have stopped working.

• Initially, the trackpad was working perfectly and just the keyboard was the problem, but now, the trackpad stopped working as well.
• After reading that a common problem is the fragility of the ribbon cable between the trackpad and keyboard, I ordered and replaced this cable, but to no avail.
• I managed to get ONE key to work on the keyboard for a moment (the “;” key) but that didn’t last long.
• I followed this video tutorial  for the battery replacement How to Upgrade / Replace the Battery in a MacBook Pro Retina 13-inch (late 2013 to early 2015)
• Update: I managed to get everything back to the initial state it was in; the trackpad working fine again, as well as the “;” key on the keyboard, but no other keys.

Given the circumstance, I am wondering if this could be something as simple as a loose connection somewhere (though I believe I have tightly secured all connections), however, I don’t believe this has anything to do with a physically faulty keyboard or trackpad, given that they both did work momentarily. I’m kindly asking if replacement of keyboard and trackpad can be avoided here.

The Apple Store isn’t much help here in the Metro Detroit area so I’m trying to fix this myself. In fact, they’re just pushing me to upgrade to a newer laptop. Super frustrating response.

Any suggestions?  =)