Check in your Netgear's logs.
If you don't know how to do this:
1. Open your browser and direct it to 192.168.0.1 (if that doesn't work, try 192.168.1.1).
2. When prompted for a username and password, use "admin" for both (default for Netgear).
3. This will then open the routers settings in the browser. Somewhere in one of these you should find a status log.
The next time this happens, open the log and copy and paste whatever it reports as the issue.
Come to think of it, I had a similar problem with a Netgear router and my ISP. Finally ended up having to replace the router with a D-Link router.