Here is something else to try.
Go to control panel.
Go to administrative tools
Go to services.
In this window, is a list of everything thats running in the background. Next to it is the description of what it does. Be suspect of anything without a description. Read through them all and see if anything jumps out at you.
You can 'turn off' something you suspect might be causing the problems and if it fixes it, your done. If not, turn it back on and move to another.
Post questions about services you don't/can't figure out or do a search on the service name to figure out what it does.
I don't recall if you said which browser you use. If you have another browser installed, does the problem happen with that browser too?
If you use IE, there is a repair tool to reset IE back to its original configuration.