Ok.
Here we encounter a software problem.
First of all are you sure that there is not any sort of vpn active on your desktop computer and there is not any sort of active download/upload on your pc?(check via task manager)
If you do so follow these instructions to remove any sort of minipoint or vpn.
1. Head to the VPN tab in windows settings and uncheck all the options
2. head to the network adapters and disable any other adapters rather than your Main one you are connected to it.
3. right click your Main adapter in the adapters page and click properties. Find the
Internet Protocol Version 4 (TCP/IPV4). Check it then click the properties and set the ip settings on automatic.
like the pictures below.
And then.
Finally check those automatic.
set your dns to automatic in the
Alternate Configuration tab.(the picture is wrong simply click the
Obtain DNS server address automatically)
Press OK and close it.
Check if the problem fixed. If it doesn't there may be some sort of hidden active connection or there is a problem between your modem and your pc.
Good luck.