Sometime my computer hangs at bios image

Hello,
sometimes my computer hangs at the very beginningi.e.,at the time when monitor displays intel pentium4,then i use to restart my computer & it then works fine.my computer is only 2 year old.i have latest hardware & good capacity hardwares.please tell me how to solve this simple problem & even sometime monitor does not show display but cpu fan,etc is working,then i use the same tricki.e.,restart my computer & it works then fine.these problems occured when i use internet on my computer from last 1month,now plz tell me how to solve problem without restarting each time,rest is ok.thanx