Ok, try this, in start, in search write msconfig, a square will pop up call System Configuration, select the tab Startup, in there you're going to see all the programs that start running when you turn on the computer, unchecked all the unnecessary programs like Realplayer, Adobe, Yahoo Messenger, after doing that hit Apply , another small screen will show up asking if you want to restart the computer, select yes. I hope this can help, sometimes there are programs that you installed on the computer and without you noticing, it automatically goes to the Strartup list, this means that it will start running as soon as the computer is turn on. You can also check
here.