My computer turn on with load window then goes black.insert the disc to format i

Hello,Hello,My computer turn on naturally and load window then goes black.insert the disc to format it did not boot from the cd,neither i can start in safe mode.i saw it says 'press F2 for set up'.that doesnt take me anywhere,only black screen appear and green lights appeared in the cpu.please help me out.thanks guys.ure great n up to the mark.help me again plz