Network comes in and out sometimes goes down router or modem?

Every now and then the internet will stop working on my PCs. I have 2 near me at all times and both will stop working, a wireless lappy and wired desky lol.

It will come back in a moment or in a little while. I havent figured out if its the router or the cable modem.

Is there some tests i can do to find out the culprit?

Bypass the router a directly wire the connection from the cable modem if it still happens then you probably have a bad modem if not then a bad router. How old are your router and modem?

If any of the modem's lights, which are lit continuously when you have Internet connectivity, start blinking when your computers lose their Internet connection, then either the modem's input cable or one of its connectors may also be bad.

Also, if your residence has cable tv, then there may be a defective splitter in a box on the outside of your residence.
I was having Internet connectivity problems simultaneously on 3 computers(1 wired, 2 wireless) 2 weeks ago, which caused the modem's "Online" light to blink(It's lit continuously when we have connectivity.). An ISP serviceman replaced the splitter on the outside of our house, and we have had zero connectivity problems since then.

Great i will check those things when it goes out again. Both the router and modem were purchased about 9 mths ago.