Windows 7 after start up lag?

My laptop running Windows & Ultimate use to start up in 20-30 seconds. Now after signing in there is a lag. Pretty much after signing in I see my desktop and that's when it happens. There is a lag that is about 20 seconds long that it just shows my desktop and the icons and then after the 20-30 seconds my desktop refreshes and the icons disappear and reappear and my network icon is no longer searching for my network and it has found my router. This is after installing AVG on my computer. any ideas what could be causing this?