Summarize the following:
If you aren’t running any programs and your hard drive light is constantly turning on and off, or you can hear the hard drive working, you may have a virus that is working in the background. If you start noticing that your computer takes significantly more time than usual to start, a virus may be slowing down the startup process. If you can’t log in to Windows, even with the correct log in information, a virus has most likely taken over the log in process. If you don’t have any programs running and your modem transfer lights are constantly blinking, you may have a virus that is transmitting data over the network.

Summary:
Check your hard drive activity. Time how long it takes your computer to boot up. Look at your modem lights.