Internet Speed Suddenly Slow

chances are you have an ADSL internet connection. The average speed they give to the consumer is 7Mbps download speed but an ADSL connection can max out at 12Mbps if you pay for it. That connection has to be split between all your device so I'd try to shut connection off to all devices but your windows 8.1 computer then try the speed test and see what you get. If you get a higher connection speed or an excellent speed it means another device is taking bandwidth that you could be using.

also go a step further and instead of resetting your router you should look on the side of the router and access it and set a new password. After that when you feel the need you can also change your wifi access password so you know only you or people you want to can get on your router. The usernames and passwords are pretty generic so a passerby could have accessed and used your wifi thus taking even more bandwidth. Also when your in your router you can go to status and wifi connections to see what devices are connected to your router.

to note ADSL connections speeds stay fairly uniform over long distances from the ISP's server near your house. While a VDSL connection will be faster but its speed drops off substantially the farther from your ISP's server near your home. I could find it on Wikipedia but there a graph with a correlation between the 2 where it actually better to have a ADSL connection at a certain distance from the nearest server. It could be that recently they redirected lines and you're now farther from the nearest server and that could be causing the drop. Since you didn't change anything to cause the sudden decrease in speed.

Also you just said you used cable internet so your not adsl but cable internet. I'd check the modem/routers logs and search for something like this
1: Aug 10 2015 17:52:12: No Ranging Response received - T3 time-out
2: Aug 10 2015 17:52:14: Ranging Request Retries exhausted
3: Aug 10 2015 17:52:14: Unicast Maintenance Ranging attempted - No response - Retries exhausted
4: Jan 01 1970 00:00:15: Cable Modem Reboot due to T4 timeout
5: Aug 10 2015 17:52:56: MIMO Event MIMO: Stored MIMO=-1 post cfg file MIMO=-1
if you see T3 and T4 timeouts it seems to be a problem with the changes in temperatures in the cable lines outside and the amplifiers that adjust the gain(signal boost) are faulty causing erros in the modems with cable on the street and giving slow connection/disconnections.
http://www.tomshardware.com/forum/21085-42-cable-internet-connection-constantly-timing info from here.

The cables outside that your cable internet run off to the server have amplifiers between them that adjust Gain(signal boost) and if your power lines actually had outages from the thunderstorms it could be that the cable amplifiers were damaged and need to be repaired/replaced. Info from

http://www.tomshardware.com/forum/21085-42-cable-internet-connection-constantly-timing
"Ellis056
Ok, I hope to shed some light on everyone's issues and pull the curtain back a little. I WAS a Charter Communications Senior System Tech. I was responsible for maintaining and repairing all mainline issues. The problem that you guys are having is, i repeat, IS a problem with your cable companies hardline distribution plant. In other words, don't waste your time or money replacing modems and or routers. If you are experiencing problems at certain times of the day, it is related to temperature. I know that sounds crazy, but hardline cable is metal. It expands and contracts with hot and cold temperatures just like any other metal substance. When this happens, the metal is either less dense(when hot) or more dense(when cold). Therefore, the signal passes differently depending on the temperature. Causing higher or lower signals when the sun comes up or goes down. Now, to battle this phenomenon, the amplifiers hanging on the lines are designed to automatically adjust the Gain (signal boost) accordingly. Now, these have to be adjusted and set up properly at least a couple times a year. Mainly due to the changing of the seasons. They can only handle so much temperature change before they start to cause serious errors. Thus your problem begins. Now keep in mind, that most newby service techs for most cable companies are clueless about anything to do with mainline issues. They are only trained to diagnose problems inside your house, and depending on their training(which usually isn't much) they probably won't even know any of this. Also, in most areas, the service techs are scared to put in a "Line Problem" because if they have missed any problems inside your house that could be causing the problem, then they are given a hard time by the system techs (who will find it). So, you should definitely insist that a line problem be put in. Also, talk with any of your neighbors and see if they are having the same issues at the same time. This will help you in your request for a line problem.

Hope this helps

Justin"

You actually lost power so there is a high chance other things on the power pole were damaged as well. I'd phone your ISP and specifically inform them about the problem occurring after the thunderstorms where some power poles in the area were brought down and that since that time the issue has cropped up. There amplifiers are no longer adjusting the cables Gain properly and its causing these issues most likely.