Computer not booting

Hello,

My O/S is windows XP.

When I start my computer first it shows a screen with options like start in Safe Mode, Start in normal mode ...if I select any one of mode or don't select anything in either case it shows windows logo for couple of seconds and then it shows a message " No Input Signal" Then again it comes back to the first screen of select mode...Its running in this loop continuously, but won't proceed further to start windows. What can I do?