well if you have any type of main browser you use open it up and look for tools or settings depending on what browser you have
after that look under extensions disable all you do not recognize
most extensions are there to guide you to sites or help you purchase things they want you too or just to annoy you until you buy some crap antivirus from their company

if after this you still have problems please look on the right hand side of your pc on the lower right side is an arrow key right click it and look at what is on if something is running you do not recognize click it off
if problem stops remember the name of such program and go to the start menu and find control panel click it open and go to uninstall programs find the program and delete it out of your pc

after all this please disk check/clean up and then defrag pc

and after all this if it still does not stop find me online and 1st try to download team viewer http://www.teamviewer.com/en/index.aspx
it does not just let people connect you have to give the password after you open it up and every time you open it it is a new password so feel safe and i hope not to see people but stuff happens!