Get Avast Antivirus Free Edition and try a boot scan. It scans everything before Windows boots up, allowing it to find sneaky spyware and other threats before they sneak into your system. You can also try looking at some malicious processes going on. Right click your start menu and click Task Manager to view all the processes. Then you have to google all of those processes to make sure that they're all ok. If you don't want to look all of them up, try downloading a program called WinUtilities, Free Edition. It scans all of your processes and tells you automatically if they are safe or malicious.