I had a similar deal on my house about 5 years after we moved in (new house), we would lose power and no breakers tripped, I'm pretty good electrical but this made no sense and sometimes power would come back and maybe not. Got to talking to a good electrician and he said is your electrical feed in conduit, well is was going to the ground. The conduit stopped about 2' under ground and unprotected after that (freakin contractor). Guess the rocks under ground will settle and cause problems digging into the cables protective coating. Replaced line into house and have no problems since. Hope this helps