Dell Laptop wont startup

I have a dell laptop which I bought in July 2014. Most of the time it will be in plugged in state although occasionally I shut it down. last day when I tried to switch it on by pressing the start button it just showed a flash screen and went off. After that no response. Not starting. I tried several tips like taking off battery.. pressing the start button for 10 seconds.. 20 seconds.. 90 seconds etc.. after un plugging the power cable etc.. But nothing works.. Bit stuck at the moment.. can anyone help