I think the root cause of this issue is as Jason ("JW") described...
I would guess that when you previously had internet service with a wifi
router, your router was placed in a relatively central location in your
home, or at least not in a corner in a concrete basement.... but, on the
other hand, most Fibre-Op installs end up being located at or near your
electrical panel... a place where is is relatively easy to bring in the
fibre from the outside and mount a few boxes on the wall...
The Actiontec modem's strength is pretty good, but the location is likely a
hinderance... but as Carter did mention, try moving the antenna a bit...
these antenna have specific coverage "patterns" and you want to try and make
sure that your furthest areas get the best coverage... or maybe the most
"critical" areas get great coverage.... you can do this with 2 people
easy enough, both on cell phones or other way to communicate and simply try
moving the antenna slowley while having a laptop or other device in the
location in question monitoring the signal strength... you can look online
for a good wifi tool; that will show strength... netstumbler worked great
with WindowsXP, but not so much with Windows7...
Alternately you can look to purchase/use a wifi router that you can more
centrally locate... some even let you use wifi for the WAN connection and
the LAN connection so you do not even need to wire it... (assuming you get
good signal in the middle of the home... this would work, although not
ideal)... I have a $20 "portable" router from china that can do that... so
I assume it can be done with at least some larger named ones...