Some keys not working on laptop keyboard

The , . / and SHIFT key (4 in a row) and the ; key (above/middle the 4 in a row) have stopped working....

they worked intermittently for a couple days, and now completely dead.
if one died when they were working intermittently, all 5 died
USB keyboard works fine
nothing was spilled on the keyboard

i've tried:

rebooting into safe mode
reattaching the ribbon to the MB connector
deleting and reinstalling the drivers


this Lenovo 3000-V100 series laptop keyboard has taken some good slams from my fists. the motherboard was replaced few months back and haven't hit it since then. i don't know if the MB is new or refurb (was replaced under warranty).

anything else i can try short of testing another keyboard?

my main concern is that it's the connector or some part on the MB as opposed to the Lenovo 3000-V100 series laptop keyboard....which is more likely given the bit of info here? i've seen people with similar issues saying a new keyboard didn't fix the problem, but most people don't report back...

any idea which it's more likely to be (mb or keyboard/ribbon)?