No light on magsafe

Sadly, if replacing the DC-In board and replacing the sleep sensor cable which you damaged didn’t fix things then you have a logic board issue!

You talk about refreshing the thermal paste in the process did you manage to damage the logic board SMC logic?

At this point I would take the logic board fully out and compare it to the iFixit guide images look for a missing or damaged component. If you don’t find anything then the charging logic its self is damaged, you’ll need to get a new logic board at that point unless you know someone with the deeper skills to fix your logic board.

As @danj said, it could be logic board damage. However, it could potentially also be a bad charger/MagSafe connection. Try giving the charger connector a clean on both the laptop and the charger. Also try wiggling the MagSafe charger for the first second of it being plugged in. It’s not too likely, but that might be the culprit. I do have one question though, does the MagSafe light show a very dim green in an unlit room?