my Win7 got this issue lately as well

It somehow recovers in 5 min, but it is so much annoying. Restart sometimes help, but another annoying as well.

Worse, my keyboard will randomly jumping letters. Finally did system restore and get the key things out. But the lost of internet or LAN is still exist from time to time.

Another possibility is you may need to replace your router. I did mine as my router is too old to meet the latest ISP requirement: DOCSIS 2.0