Though it may seem that I am stating the same terminology, troubleshooting is a logical process of elimination. I could talk in terms of DNS, BIND, TCP/IP stacks ect... but most would not understand what I am saying so, I will put it in layman terms.
First, one of the possible scenarios that causes a modem/router to lose "block sync".
Power fluxuation at the electrical outlet
Let me explain if there has been any power fluxuation in the A/C (Alternating Current) outlet (your electrical outlet) the modem could lock up and not be able to respond with the signal coming from the network servers, hence the power cycling of the modem/router and the computer.
I know what you’re going to say, I didn't see any "power fluxuation", here’s the answer: "you don't need to". The power that is produced from your electrical outlet is not a steady 120 volts of electricity, hence the name A/C (Alternating Current). The ranges of A/C (Alternating Current) can be from 130 volts to 90 volts ±5% at any given time.
Picture a roller coaster, --->/\/\/\/\/\/\<--- this is an example of how alternating current looks on a scope the middle line (where the arrows are) is where 0 (zero) is at, the human eye can not see these fluxuations in power (because the waves of current are moving too fast) but an electronic piece of equipment can. Electronic equipment can be (and is) very sensitive to a spike or drop in electrical power out of normal ranges. Now, here in the good old U.S. of A. the average A/C outlet "should" produce 110 volts of electricity, does it? NO! I can walk around my house and get ranges from 95 volts to 115 volts depending on many variables.
The ultimate solution is to purchase an Uninterruptible Power Supply (UPS), which is a (battery backup) of power for your computer, modem and router. This way if there is ever a large power fluxuation or outage the UPS maintains your current power levels and you can shut down your system normally without fear of hurting anything.
I don’t have a (UPS) or I'm not going to buy a (UPS), well then you are stuck doing the following procedures to get everything synchronized to get back on the internet. Shut down the computer, "NOT" restart the computer, let it shut down completely. Unplug the modem and router and leave it unplugged for at the very least 15 seconds, look at your watch, (you would not believe how long 15 seconds can be). Now, plug-in the modem first and "WAIT" at least two minutes, (this depends on the type of modem you have) again look at your watch. After letting the modem sync, then plug in your router and "WAIT" at least one minute, again (this depends on the type of router you have) After letting the router sync then turn your computer on.
If you don't have a router, just eliminate the middle step.
Why do I have to do it this way?
First, every piece of equipment cycles through at different phases, a modem has to cycle through it's power up phase (checking internal components), then calls out to get network information before it is synchronized, a router automatically expects the network information and modem to be ready so it can just pick up the information and channel it through. Where a modem has to do extra steps of powering up and retrieving network information, the router thinks the information is already in place, so it doesn't need the extra time for the power up phase and within (sometimes seconds) it is powered up and is trying to pull network information while the modem is still in the cycle of it's power up phase, they become out of synchronization and no connection.
To put in simpler terms, let’s compare the modem to your computer; does your computer instantly go to the desktop when you turn it on? NO! It checks all kinds of hardware first, and then it checks the software etc... then it starts booting to your desktop which can take minutes, well the power cycling of a modem is comparable, it has to check that all the hardware is working, check it's firmware, then retrieves a network connection, finally it is ready to send network information.
I hope this was helpful in understanding "ONE" of many possible scenarios of why your computer modem and router can loose connection. When I have time I will post other possible scenarios to try and help others to understand what can happen and why they can loose a network connection.