Yahoo mail logs me out every 30 seconds

bummer, there are a lot of potential causes for this. Bad cable, bad firmware, bad driver, bad router and the problem does not have to be on your machine, It can be on a machine plugged into your network and not the actual one you are trying to get to work.

there are some tools you can use to help:

microsoft network monitor can be used to make a sniffer trace, you install it on your local machine and trace all the traffic until you hit the error. Then you stop the trace and look at the packets and see who sent them. (from your machine or not your machine) It sounds like your connection is being closed because incorrect network packets were not received. Mostly, this happens when there has been a extension to definition of a protocol and one side is using the update and the other is not. Or just bugs where a network packet is blocked or dropped.

again there are many causes, take a quick look at this tool netstat.exe it can be run from a elevated command prompt on windows and is included.

start cmd.exe as a admin (windows key+x then A)
netstat.exe -a

it will display al of your various tcp connections, their local address and winsock port and where they are connected to (foreign address) and the State of the socket connection.

you will be looking for large number of connections or large numbers in a TIME_WAIT state.

if windows thinks you have too many (because of a malware) they will attempt to slow the connections down or block new connections.

use
netstat -b

this will return the name of the program that is making the connections.
Sometimes this will be useful to find something that you did not even know it was running. I just ran it now to check the syntax and found I have some streaming software running that I had turned off yesterday, now I found it was restarted via task schedule.

- firewall software can block one side of a network communication, and it results in the other side not getting the correct response, it then waits until its programmed timeout. After the timeout it sends a connection reset signal on the assumption that a packet was lost.

- old firmware in routers can mess with packets

- old drivers for your ethernet card can be written to a older spec or just have bugs in them. Look at the rash of windows 8.0 problems with the bug in the intel ethernet drivers. one little spec change caused havoc.

You might also look in your eventlog for to see if windows is throttling you TCP/IP connections. (just a potential cause if all of your connections get tied up and you have to have TIME_WAIT period expire. i think it is 30 seconds and it does 5 of them. (sorry, its been too long for me to remember off the top of my head)

you might consider isolating your system, a direct connection from 1 machine directly wired via your ethernet from your motherboard to your cable modem
(bypass router and any other local network noise) to see if you have the same problem. Then turn off various network services, update drivers ...

kind of takes a while.