No Internet but modem is fine?

I got comcast hooked up a week ago and it was fine for a day, then my kid tried to install IE 8 from a flash drive (w/out permission) and when I got on to install a webcam the pc said something was already installing. I didn't know what it was so I was waiting on someone to call and my kid decided to hop on and try to delete or cancel it so she wouldn't get in trouble, when she couldn't get it done she restored my pc to a time before I got my comcast internet. All of a sudden the pc went into safe mode and there was a big black frame around the window. She got scared and powered off the pc. Now when I turn it on my modem lights are fine but I cannot get online. She said it was trying to dialup but we have a cable connection. I took my tower to a friends and it wouldn't connect to their internet either. I had someone delete all my programs and reinstall them from the discs in the hopes it was a glitch but still no internet....any ideas???? Oh, no router or laptop or anything just a desktop that's about 5yrs old.