BIOS not appearing

Hi,

I am using dell laptop from 2 and half years. It encountered a problem which i am struggling to detect. It is starting but not cross first screen. I tried a lot to format by using F2, F12 but in vain. Although F2, F12 buttons are working but screen is coming back to inspiron. It is not starting in safe mode also. I pressed the power button after removing battery and AC adaptor but no remedy at all. I check Hard drive also. It is working fine. Please suggest, what next should i do?