Problems like the ones you describe are FREQUENTLY caused by bad Domain Name Servers (DNS).
ISPs (Internet Service Providers) generally make several different Domain Name Servers available, and their tech support people are often aware of some that aren't very reliable.
If your PC (or your router) is configured to ask an unreliable DNS for IP addresses, then sometimes things will work ok and at other times things will NOT work OK.
If you set up a TCP connection to some web site, torrent, or other service while your DNS is working OK, then that connection is likely to continue working OK for a while, even if the DNS goes down, but NEW connections won't start up until the DNS gets fixed. It is commonplace for ISP DNS hardware to overheat or become overloaded and fail from time to time.
You can test this theory with a little advanced preparation: During a period when everything is working OK, ping a few of your favorite web sites, and WRITE DOWN the numeric IP addresses on a convenient piece of paper.
Then, during a period when you are experiencing trouble as you described. verify that you can no longer ping those same websites by DNS name. Follow up with a test to see if you can ping those same web sites through the numeric IP address. If you CAN ping them thru the numeric IP address but NOT by name, you've got a faulty DNS. In that case you need to complain to your DNS provider. This is generally your ISP. Or you can choose one of the free DNS providers like "OpenDNS".
I hope this helps!
-Peabody-
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