Since some of those clients are quite different from one another, it could be due to some other safety app installed which is causing this e.g. AntiVirus or AntiSpyware.

I don't think your ISP has the ability or the interest to completely freeze your computer.

Edit: regarding below post by LOTR. Have you installed any network connection monitoring program, antivirus, antimalware or similar program given to you by your ISP?