I read here that there is a diagnostic power on diagnostic test by holding down the FN key and pressing the power button. By doing this I managed to run the Hardware Diagnostic tests OK.
http://en.community.dell.com/support-forums/laptop/f/3518/p/18632864/18755850.aspx
try running diagnostics . press Fn + Power to invoke the Pre-Boot Self assessment test. it will tell you if there's a problem w/your hardware. If everything passes that means you have a software problem.