2010 Buick enclave three a bunch of codes then wont start

I just bought a 2010 Buick enclave and a bit after buying it
my traction control light came on and it said service
stibilitrac then the check engine light came on and then abs
light, not all 3 were on at the same times they were all
random I took it to my mechanic and he said possible
timing but I had to take it to a dealer for that so I did and
they said it could be timing or sludge in the engine and I
needed an engine replacement. I am some fuel system
cleaner threw it and the lights went away for a while but
they just came back on yesterday. Traction control then
check engine then abs and then brake light. Took back to
my mechanic and he said he didn't think the computer was
communicating right and may need reprogrammed or
replaced. And now this morning it wouldn't start at all. What
is going on?