Internet speed slowing down and no activity

I have an AMD processor, which I have been using for almost 2 years. For the past 2-3 months, my internet speed has been getting down gradually after a period of 2-3 hours and even no activity in between and I have to again restart the modem but again after 10-15 minutes same thing. I am using BSNL connection. I have asked them about this and they have done everything they could including changing the line and modem, but to no avail. They say its electrical interference, which is causing the net to slow down and we cant do anything. Is it due to AMD processor. There are no spywares or malwares as I have scanned the system with all the latest security tools and nothing came. The download stream during that time goes as low as 5-6 and even after restarting modem, maximum 10-11 and then no activity in the net. Is it happening because processor heating up and causing the net to go down? Kindly help as I am suffering very much because of this