The implication is that they simply went dark during their normal operations.
The last communication would presumably be something along the lines of "Acknowledged. Will do", in response to Burke's instruction to go "check out these coordinates".
Burke looked down at his slim-line, secured briefcase. It has to be
checked out. Fast. All communications are down. They’ve been down too
long for the interruption to be due to equipment failure. Acheron’s
been in business for years. They’re experienced people, and they have
appropriate backup systems. Maybe they’re working on fixing the
problem right now. But it’s been no-go dead silence for too long.
People are getting nervous. Somebody has to go and check it out in
person. It’s the only way to quiet the nervous Nellies.
Aliens: Official Novelisation
This is backed up by the Aliens: Colonial Marines Technical Manual factbook which has a "report" on the events that occurred. They make no mention of any abnormal communications other than the receiver going off the air.
"Now, see this file here. Carter J.Burke sends an order dated 6/12/79 to Hadley's Hope colony complex, blah blah... look here - he's requesting that s cane one check out a bunch of coordinates, here, just beyond the Ilyium mountain range. Bingo! So what happens next?"
"Presumably, someone checks out the coordinates. Three weeks later the colony transmitters go off the air. The company then places a formal request to the UA and United States Space Command for a Marine taskforce to scope out the colony-"
That all being said, Carter Burke is a known liar and WY could easily have received a whole bunch of radio messages begging for help and just not told anyone about it.