My computer is turn on start bios ends there.

Hello,
i own hp probook 4510s laptop, first i used to install window seven, then i used to install ubuntu dual boot with window seven but immedietly after complete ubuntu installation computer ask to restart, i respond ok but after then it fail to start correctly, it turned on then bios take up the job and stay there, so even when i tried to insert bootable cd/dvd it fails since it seems it does not reach any far stage after the bios.#

assist me because i am a student and i used my laptop as a main tool for my studies.