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Change the power plan (Disable power−saving mode)
If you are a Windows user (especially if you have recently upgraded your computer to Windows 8 or Windows 10) and your Internet speed has become very slow, the power plan settings might be the problem. Windows 8(.1) and Windows 10 try to save power wherever it's possible by limiting the hardware components (one of which is the network card). To change the power plan (disable power-saving mode), and hopefully resolve the "my internet connection is too slow" issue follow the steps below:
Go to the start menu and type device manager.
Once the Device Manager opens, click on Network adapters, right click on your Wi-Fi adapter and click on Properties;
Click on the Power management tab (the last one) uncheck Allow the computer to turn off this device to save power;
Click on the Advanced tab;
Change the values of:
Afterburner to Enable
AP Compatibility Mode to Higher Performance
Minimum Power Consumption to Disabled
Power output to 100%
Power Save Mode to Disabled
Reboot the computer and once it turns on, go to speedtest.net to test your Internet speed.
Note: The options in step 5 may vary from computer to computer or Wi-Fi adapter.