Browser problems

Hi everyone! I have 2 comps connected to external modem. both on xp, both have been running great for 1 yr until yesterday. One, comp A could access internet, but comp B could not, it was clearly online(ping test) but web page would not open, i used internet explorer and firefox. I used msconfig to start up in normal and now everything works. How did that fix the problem? Crazy question I know, an why I did that I have no idea!! lol can anyone tell me why?
Thanks,
Matti

 

No one knows?