A few questions.
Have you changed anything before it began happening? Put a splitter somewhere, added a tv, or anything like that.
What does the lights on the modem look like when it goes down? If you can post the modems info like the SNR, return and all that could help.
I dont think its your computer (though could be something got by your security). Unscrew the cable from both the mdm and wall and screw it back in snug (hand tight only).
If there is a tv at the mdms location also that is off a splitter unplug the splitter and go directetly into the splitter.